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 $197.90   3.843%   $205.5053   $205.51   $205.50   $205.50  
  Purchase #2 $88.81   5.792%   $93.9539   $93.95   $93.95   $94.00  
  Purchase #3 $83.33   5.754%   $88.1248   $88.12   $88.10   $88.10  
  Purchase #4 $110.31   3.683%   $114.3727   $114.37   $114.35   $114.40  
  Purchase #5 $218.46   4.630%   $228.5747   $228.57   $228.55   $228.60  
  Purchase #6 $146.74   9.502%   $160.6832   $160.68   $160.70   $160.70  
  Purchase #7 $57.75   4.730%   $60.4816   $60.48   $60.50   $60.50  
  7 purchase totals = $903.30       $951.6962   $951.68   $951.65   $951.80