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 $239.70   8.460%   $259.9786   $259.98   $260.00   $260.00  
  Purchase #2 $149.97   11.151%   $166.6932   $166.69   $166.70   $166.70  
  Purchase #3 $97.85   3.562%   $101.3354   $101.34   $101.35   $101.30  
  Purchase #4 $54.53   8.703%   $59.2757   $59.28   $59.30   $59.30  
  Purchase #5 $215.53   4.417%   $225.05   $225.05   $225.05   $225.10  
  Purchase #6 $229.42   12.177%   $257.3565   $257.36   $257.35   $257.40  
  Purchase #7 $23.76   9.496%   $26.0162   $26.02   $26.00   $26.00  
  7 purchase totals = $1,010.76       $1,095.7056   $1,095.72   $1,095.75   $1,095.80