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 $248.52   6.319%   $264.224   $264.22   $264.20   $264.20  
  Purchase #2 $240.29   8.425%   $260.5344   $260.53   $260.55   $260.50  
  Purchase #3 $54.86   6.163%   $58.241   $58.24   $58.25   $58.20  
  Purchase #4 $88.99   13.782%   $101.2546   $101.25   $101.25   $101.30  
  Purchase #5 $197.30   3.595%   $204.3929   $204.39   $204.40   $204.40  
  Purchase #6 $133.73   13.584%   $151.8959   $151.90   $151.90   $151.90  
  Purchase #7 $188.39   12.801%   $212.5058   $212.51   $212.50   $212.50  
  7 purchase totals = $1,152.08       $1,253.0486   $1,253.04   $1,253.05   $1,253.00