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 $87.62   7.426%   $94.1267   $94.13   $94.15   $94.10  
  Purchase #2 $244.80   7.285%   $262.6337   $262.63   $262.65   $262.60  
  Purchase #3 $158.50   13.662%   $180.1543   $180.15   $180.15   $180.20  
  Purchase #4 $227.62   3.767%   $236.1944   $236.19   $236.20   $236.20  
  Purchase #5 $20.50   5.780%   $21.6849   $21.68   $21.70   $21.70  
  Purchase #6 $34.39   9.412%   $37.6268   $37.63   $37.65   $37.60  
  Purchase #7 $121.94   9.689%   $133.7548   $133.75   $133.75   $133.80  
  7 purchase totals = $895.37       $966.1756   $966.16   $966.25   $966.20