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 $53.46   7.809%   $57.6347   $57.63   $57.65   $57.60  
  Purchase #2 $216.29   9.141%   $236.0611   $236.06   $236.05   $236.10  
  Purchase #3 $178.62   4.698%   $187.0116   $187.01   $187.00   $187.00  
  Purchase #4 $172.26   3.596%   $178.4545   $178.45   $178.45   $178.50  
  Purchase #5 $116.63   5.168%   $122.6574   $122.66   $122.65   $122.70  
  Purchase #6 $147.44   7.503%   $158.5024   $158.50   $158.50   $158.50  
  Purchase #7 $199.45   5.271%   $209.963   $209.96   $209.95   $210.00  
  7 purchase totals = $1,084.15       $1,150.2847   $1,150.27   $1,150.25   $1,150.40