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 $61.27   7.756%   $66.0221   $66.02   $66.00   $66.00  
  Purchase #2 $177.27   6.487%   $188.7695   $188.77   $188.75   $188.80  
  Purchase #3 $126.51   11.213%   $140.6956   $140.70   $140.70   $140.70  
  Purchase #4 $217.63   9.188%   $237.6258   $237.63   $237.65   $237.60  
  Purchase #5 $59.86   5.505%   $63.1553   $63.16   $63.15   $63.20  
  Purchase #6 $114.31   8.786%   $124.3533   $124.35   $124.35   $124.40  
  Purchase #7 $214.77   10.340%   $236.9772   $236.98   $237.00   $237.00  
  7 purchase totals = $971.62       $1,057.5988   $1,057.61   $1,057.60   $1,057.70