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 $227.63   11.579%   $253.9873   $253.99   $254.00   $254.00  
  Purchase #2 $117.39   12.715%   $132.3161   $132.32   $132.30   $132.30  
  Purchase #3 $61.33   13.786%   $69.785   $69.79   $69.80   $69.80  
  Purchase #4 $162.40   5.311%   $171.0251   $171.03   $171.05   $171.00  
  Purchase #5 $205.83   12.160%   $230.8589   $230.86   $230.85   $230.90  
  Purchase #6 $28.26   13.772%   $32.152   $32.15   $32.15   $32.20  
  Purchase #7 $248.29   5.504%   $261.9559   $261.96   $261.95   $262.00  
  7 purchase totals = $1,051.13       $1,152.0803   $1,152.10   $1,152.10   $1,152.20