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 $245.38   3.165%   $253.1463   $253.15   $253.15   $253.10  
  Purchase #2 $62.64   4.764%   $65.6242   $65.62   $65.60   $65.60  
  Purchase #3 $241.60   6.832%   $258.1061   $258.11   $258.10   $258.10  
  Purchase #4 $38.50   9.630%   $42.2076   $42.21   $42.20   $42.20  
  Purchase #5 $171.85   4.758%   $180.0266   $180.03   $180.05   $180.00  
  Purchase #6 $60.65   5.473%   $63.9694   $63.97   $63.95   $64.00  
  Purchase #7 $143.27   11.468%   $159.7002   $159.70   $159.70   $159.70  
  7 purchase totals = $963.89       $1,022.7804   $1,022.79   $1,022.75   $1,022.70