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 $85.52   12.409%   $96.1322   $96.13   $96.15   $96.10  
  Purchase #2 $54.40   12.662%   $61.2881   $61.29   $61.30   $61.30  
  Purchase #3 $62.74   8.301%   $67.948   $67.95   $67.95   $67.90  
  Purchase #4 $90.56   4.865%   $94.9657   $94.97   $94.95   $95.00  
  Purchase #5 $130.45   7.726%   $140.5286   $140.53   $140.55   $140.50  
  Purchase #6 $246.67   9.715%   $270.634   $270.63   $270.65   $270.60  
  Purchase #7 $103.78   5.546%   $109.5356   $109.54   $109.55   $109.50  
  7 purchase totals = $774.12       $841.0322   $841.04   $841.10   $840.90