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 $63.99   3.110%   $65.9801   $65.98   $66.00   $66.00  
  Purchase #2 $110.83   12.839%   $125.0595   $125.06   $125.05   $125.10  
  Purchase #3 $51.72   10.847%   $57.3301   $57.33   $57.35   $57.30  
  Purchase #4 $132.64   10.235%   $146.2157   $146.22   $146.20   $146.20  
  Purchase #5 $180.45   7.678%   $194.305   $194.31   $194.30   $194.30  
  Purchase #6 $121.62   3.210%   $125.524   $125.52   $125.50   $125.50  
  Purchase #7 $43.32   9.539%   $47.4523   $47.45   $47.45   $47.50  
  7 purchase totals = $704.57       $761.8667   $761.87   $761.85   $761.90