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 $214.84   9.514%   $235.2799   $235.28   $235.30   $235.30  
  Purchase #2 $116.98   13.692%   $132.9969   $133.00   $133.00   $133.00  
  Purchase #3 $216.48   6.505%   $230.562   $230.56   $230.55   $230.60  
  Purchase #4 $122.45   8.368%   $132.6966   $132.70   $132.70   $132.70  
  Purchase #5 $101.69   5.694%   $107.4802   $107.48   $107.50   $107.50  
  Purchase #6 $217.70   10.486%   $240.528   $240.53   $240.55   $240.50  
  Purchase #7 $116.82   12.371%   $131.2718   $131.27   $131.25   $131.30  
  7 purchase totals = $1,106.96       $1,210.8154   $1,210.82   $1,210.85   $1,210.90