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 $64.83   8.271%   $70.1921   $70.19   $70.20   $70.20  
  Purchase #2 $156.88   13.303%   $177.7497   $177.75   $177.75   $177.70  
  Purchase #3 $219.68   11.816%   $245.6374   $245.64   $245.65   $245.60  
  Purchase #4 $61.44   12.127%   $68.8908   $68.89   $68.90   $68.90  
  Purchase #5 $24.57   5.263%   $25.8631   $25.86   $25.85   $25.90  
  Purchase #6 $231.76   7.716%   $249.6426   $249.64   $249.65   $249.60  
  Purchase #7 $43.26   10.865%   $47.9602   $47.96   $47.95   $48.00  
  7 purchase totals = $802.42       $885.9359   $885.93   $885.95   $885.90