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 $158.71   3.398%   $164.103   $164.10   $164.10   $164.10  
  Purchase #2 $55.31   12.740%   $62.3565   $62.36   $62.35   $62.40  
  Purchase #3 $23.66   12.224%   $26.5522   $26.55   $26.55   $26.60  
  Purchase #4 $151.49   7.673%   $163.1138   $163.11   $163.10   $163.10  
  Purchase #5 $5.76   3.758%   $5.9765   $5.98   $6.00   $6.00  
  Purchase #6 $200.75   10.533%   $221.895   $221.90   $221.90   $221.90  
  Purchase #7 $133.51   13.215%   $151.1533   $151.15   $151.15   $151.20  
  7 purchase totals = $729.19       $795.1503   $795.15   $795.15   $795.30