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 $67.74   13.291%   $76.7433   $76.74   $76.75   $76.70  
  Purchase #2 $136.39   10.375%   $150.5405   $150.54   $150.55   $150.50  
  Purchase #3 $250.98   8.487%   $272.2807   $272.28   $272.30   $272.30  
  Purchase #4 $36.54   13.793%   $41.58   $41.58   $41.60   $41.60  
  Purchase #5 $209.88   4.742%   $219.8325   $219.83   $219.85   $219.80  
  Purchase #6 $41.42   13.180%   $46.8792   $46.88   $46.90   $46.90  
  Purchase #7 $170.81   8.318%   $185.018   $185.02   $185.00   $185.00  
  7 purchase totals = $913.76       $992.8742   $992.87   $992.95   $992.80