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 $58.85   12.467%   $66.1868   $66.19   $66.20   $66.20  
  Purchase #2 $36.69   6.497%   $39.0737   $39.07   $39.05   $39.10  
  Purchase #3 $135.70   6.261%   $144.1962   $144.20   $144.20   $144.20  
  Purchase #4 $120.86   10.340%   $133.3569   $133.36   $133.35   $133.40  
  Purchase #5 $59.60   13.452%   $67.6174   $67.62   $67.60   $67.60  
  Purchase #6 $180.51   10.709%   $199.8408   $199.84   $199.85   $199.80  
  Purchase #7 $97.62   11.352%   $108.7018   $108.70   $108.70   $108.70  
  7 purchase totals = $689.83       $758.9736   $758.98   $758.95   $759.00