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 $183.57   11.293%   $204.3006   $204.30   $204.30   $204.30  
  Purchase #2 $182.51   13.736%   $207.5796   $207.58   $207.60   $207.60  
  Purchase #3 $239.96   9.744%   $263.3417   $263.34   $263.35   $263.30  
  Purchase #4 $73.81   3.378%   $76.3033   $76.30   $76.30   $76.30  
  Purchase #5 $107.53   12.587%   $121.0648   $121.06   $121.05   $121.10  
  Purchase #6 $75.73   4.149%   $78.872   $78.87   $78.85   $78.90  
  Purchase #7 $49.73   4.406%   $51.9211   $51.92   $51.90   $51.90  
  7 purchase totals = $912.84       $1,003.3831   $1,003.37   $1,003.35   $1,003.40