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 $62.96   11.441%   $70.1633   $70.16   $70.15   $70.20  
  Purchase #2 $54.98   3.153%   $56.7135   $56.71   $56.70   $56.70  
  Purchase #3 $239.76   10.228%   $264.2827   $264.28   $264.30   $264.30  
  Purchase #4 $224.62   11.450%   $250.339   $250.34   $250.35   $250.30  
  Purchase #5 $12.77   4.581%   $13.355   $13.36   $13.35   $13.40  
  Purchase #6 $98.89   5.279%   $104.1104   $104.11   $104.10   $104.10  
  Purchase #7 $195.50   10.427%   $215.8848   $215.88   $215.90   $215.90  
  7 purchase totals = $889.48       $974.8487   $974.84   $974.85   $974.90