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 $47.83   6.639%   $51.0054   $51.01   $51.00   $51.00  
  Purchase #2 $240.63   8.359%   $260.7443   $260.74   $260.75   $260.70  
  Purchase #3 $204.37   7.653%   $220.0104   $220.01   $220.00   $220.00  
  Purchase #4 $165.33   7.345%   $177.4735   $177.47   $177.45   $177.50  
  Purchase #5 $61.84   13.588%   $70.2428   $70.24   $70.25   $70.20  
  Purchase #6 $222.84   5.210%   $234.45   $234.45   $234.45   $234.50  
  Purchase #7 $208.92   13.812%   $237.776   $237.78   $237.80   $237.80  
  7 purchase totals = $1,151.76       $1,251.7024   $1,251.70   $1,251.70   $1,251.70