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 $117.99   12.506%   $132.7458   $132.75   $132.75   $132.70  
  Purchase #2 $45.68   12.352%   $51.3224   $51.32   $51.30   $51.30  
  Purchase #3 $237.33   4.434%   $247.8532   $247.85   $247.85   $247.90  
  Purchase #4 $119.36   5.537%   $125.969   $125.97   $125.95   $126.00  
  Purchase #5 $88.64   12.332%   $99.5711   $99.57   $99.55   $99.60  
  Purchase #6 $111.85   9.610%   $122.5988   $122.60   $122.60   $122.60  
  Purchase #7 $198.44   11.467%   $221.1951   $221.20   $221.20   $221.20  
  7 purchase totals = $919.29       $1,001.2554   $1,001.26   $1,001.20   $1,001.30