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 $55.86   6.153%   $59.2971   $59.30   $59.30   $59.30  
  Purchase #2 $11.51   12.393%   $12.9364   $12.94   $12.95   $12.90  
  Purchase #3 $177.69   10.158%   $195.7398   $195.74   $195.75   $195.70  
  Purchase #4 $22.88   9.271%   $25.0012   $25.00   $25.00   $25.00  
  Purchase #5 $149.73   11.300%   $166.6495   $166.65   $166.65   $166.60  
  Purchase #6 $162.60   11.749%   $181.7039   $181.70   $181.70   $181.70  
  Purchase #7 $97.48   4.605%   $101.969   $101.97   $101.95   $102.00  
  7 purchase totals = $677.75       $743.2969   $743.30   $743.30   $743.20