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 $249.99   4.716%   $261.7795   $261.78   $261.80   $261.80  
  Purchase #2 $80.53   10.444%   $88.9406   $88.94   $88.95   $88.90  
  Purchase #3 $222.37   11.520%   $247.987   $247.99   $248.00   $248.00  
  Purchase #4 $211.31   6.151%   $224.3077   $224.31   $224.30   $224.30  
  Purchase #5 $39.43   3.236%   $40.706   $40.71   $40.70   $40.70  
  Purchase #6 $84.85   8.813%   $92.3278   $92.33   $92.35   $92.30  
  Purchase #7 $79.65   11.650%   $88.9292   $88.93   $88.95   $88.90  
  7 purchase totals = $968.13       $1,044.9778   $1,044.99   $1,045.05   $1,044.90