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 $151.88   7.346%   $163.0371   $163.04   $163.05   $163.00  
  Purchase #2 $225.63   3.110%   $232.6471   $232.65   $232.65   $232.60  
  Purchase #3 $97.31   7.635%   $104.7396   $104.74   $104.75   $104.70  
  Purchase #4 $142.98   3.661%   $148.2145   $148.21   $148.20   $148.20  
  Purchase #5 $50.55   6.162%   $53.6649   $53.66   $53.65   $53.70  
  Purchase #6 $197.59   3.735%   $204.97   $204.97   $204.95   $205.00  
  Purchase #7 $78.56   8.240%   $85.0333   $85.03   $85.05   $85.00  
  7 purchase totals = $944.50       $992.3065   $992.30   $992.30   $992.20