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 $243.98   3.227%   $251.8532   $251.85   $251.85   $251.90  
  Purchase #2 $196.95   7.108%   $210.9492   $210.95   $210.95   $210.90  
  Purchase #3 $26.91   8.269%   $29.1352   $29.14   $29.15   $29.10  
  Purchase #4 $119.44   13.852%   $135.9848   $135.98   $136.00   $136.00  
  Purchase #5 $156.98   3.471%   $162.4288   $162.43   $162.45   $162.40  
  Purchase #6 $69.46   4.673%   $72.7059   $72.71   $72.70   $72.70  
  Purchase #7 $82.69   11.855%   $92.4929   $92.49   $92.50   $92.50  
  7 purchase totals = $896.41       $955.5500   $955.55   $955.60   $955.50