Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.43   8.483%   $267.3347   $267.33   $267.35   $267.30  
  Purchase #2 $188.67   9.526%   $206.6427   $206.64   $206.65   $206.60  
  Purchase #3 $195.60   11.139%   $217.3879   $217.39   $217.40   $217.40  
  Purchase #4 $143.96   11.827%   $160.9861   $160.99   $161.00   $161.00  
  Purchase #5 $153.98   13.285%   $174.4362   $174.44   $174.45   $174.40  
  Purchase #6 $220.89   13.759%   $251.2823   $251.28   $251.30   $251.30  
  Purchase #7 $187.53   5.406%   $197.6679   $197.67   $197.65   $197.70  
  7 purchase totals = $1,337.06       $1,475.7378   $1,475.74   $1,475.80   $1,475.70