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 $227.30   11.467%   $253.3645   $253.36   $253.35   $253.40  
  Purchase #2 $93.86   8.593%   $101.9254   $101.93   $101.95   $101.90  
  Purchase #3 $83.38   13.812%   $94.8964   $94.90   $94.90   $94.90  
  Purchase #4 $219.59   5.869%   $232.4777   $232.48   $232.50   $232.50  
  Purchase #5 $99.91   5.433%   $105.3381   $105.34   $105.35   $105.30  
  Purchase #6 $238.63   6.803%   $254.864   $254.86   $254.85   $254.90  
  Purchase #7 $89.46   3.206%   $92.3281   $92.33   $92.35   $92.30  
  7 purchase totals = $1,052.13       $1,135.1942   $1,135.20   $1,135.25   $1,135.20