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 $87.72   13.573%   $99.6262   $99.63   $99.65   $99.60  
  Purchase #2 $210.76   11.686%   $235.3894   $235.39   $235.40   $235.40  
  Purchase #3 $71.40   4.793%   $74.8222   $74.82   $74.80   $74.80  
  Purchase #4 $60.96   11.487%   $67.9625   $67.96   $67.95   $68.00  
  Purchase #5 $133.58   9.378%   $146.1071   $146.11   $146.10   $146.10  
  Purchase #6 $45.48   5.623%   $48.0373   $48.04   $48.05   $48.00  
  Purchase #7 $24.39   3.832%   $25.3246   $25.32   $25.30   $25.30  
  7 purchase totals = $634.29       $697.2693   $697.27   $697.25   $697.20