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 $55.38   11.428%   $61.7088   $61.71   $61.70   $61.70  
  Purchase #2 $228.97   5.665%   $241.9412   $241.94   $241.95   $241.90  
  Purchase #3 $121.97   5.481%   $128.6552   $128.66   $128.65   $128.70  
  Purchase #4 $37.36   5.115%   $39.271   $39.27   $39.25   $39.30  
  Purchase #5 $162.66   12.153%   $182.4281   $182.43   $182.45   $182.40  
  Purchase #6 $223.59   10.834%   $247.8137   $247.81   $247.80   $247.80  
  Purchase #7 $78.58   7.263%   $84.2873   $84.29   $84.30   $84.30  
  7 purchase totals = $908.51       $986.1053   $986.11   $986.10   $986.10