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 $96.70   6.779%   $103.2553   $103.26   $103.25   $103.30  
  Purchase #2 $61.55   9.720%   $67.5327   $67.53   $67.55   $67.50  
  Purchase #3 $201.56   8.239%   $218.1665   $218.17   $218.15   $218.20  
  Purchase #4 $35.38   11.312%   $39.3822   $39.38   $39.40   $39.40  
  Purchase #5 $60.50   10.651%   $66.9439   $66.94   $66.95   $66.90  
  Purchase #6 $54.71   13.700%   $62.2053   $62.21   $62.20   $62.20  
  Purchase #7 $129.46   8.796%   $140.8473   $140.85   $140.85   $140.80  
  7 purchase totals = $639.86       $698.3332   $698.34   $698.35   $698.30