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 $72.59   4.699%   $76.001   $76.00   $76.00   $76.00  
  Purchase #2 $124.40   12.253%   $139.6427   $139.64   $139.65   $139.60  
  Purchase #3 $96.64   4.832%   $101.3096   $101.31   $101.30   $101.30  
  Purchase #4 $39.64   3.349%   $40.9675   $40.97   $40.95   $41.00  
  Purchase #5 $67.35   9.823%   $73.9658   $73.97   $73.95   $74.00  
  Purchase #6 $44.49   13.112%   $50.3235   $50.32   $50.30   $50.30  
  Purchase #7 $161.29   4.787%   $169.011   $169.01   $169.00   $169.00  
  7 purchase totals = $606.40       $651.2211   $651.22   $651.15   $651.20