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 $84.72   9.218%   $92.5295   $92.53   $92.55   $92.50  
  Purchase #2 $203.31   11.640%   $226.9753   $226.98   $227.00   $227.00  
  Purchase #3 $60.37   3.670%   $62.5856   $62.59   $62.60   $62.60  
  Purchase #4 $111.97   7.716%   $120.6096   $120.61   $120.60   $120.60  
  Purchase #5 $72.39   5.112%   $76.0906   $76.09   $76.10   $76.10  
  Purchase #6 $150.61   13.271%   $170.5975   $170.60   $170.60   $170.60  
  Purchase #7 $42.26   13.870%   $48.1215   $48.12   $48.10   $48.10  
  7 purchase totals = $725.63       $797.5096   $797.52   $797.55   $797.50