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 $247.67   11.761%   $276.7985   $276.80   $276.80   $276.80  
  Purchase #2 $117.41   7.498%   $126.2134   $126.21   $126.20   $126.20  
  Purchase #3 $112.69   3.157%   $116.2476   $116.25   $116.25   $116.20  
  Purchase #4 $221.59   5.668%   $234.1497   $234.15   $234.15   $234.10  
  Purchase #5 $211.57   7.529%   $227.4991   $227.50   $227.50   $227.50  
  Purchase #6 $51.25   11.522%   $57.155   $57.16   $57.15   $57.20  
  Purchase #7 $119.61   3.823%   $124.1827   $124.18   $124.20   $124.20  
  7 purchase totals = $1,081.79       $1,162.2460   $1,162.25   $1,162.25   $1,162.20