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 $24.34   3.612%   $25.2192   $25.22   $25.20   $25.20  
  Purchase #2 $51.78   3.124%   $53.3976   $53.40   $53.40   $53.40  
  Purchase #3 $106.94   11.351%   $119.0788   $119.08   $119.10   $119.10  
  Purchase #4 $71.88   10.496%   $79.4245   $79.42   $79.40   $79.40  
  Purchase #5 $223.73   12.273%   $251.1884   $251.19   $251.20   $251.20  
  Purchase #6 $236.41   4.549%   $247.1643   $247.16   $247.15   $247.20  
  Purchase #7 $242.71   3.588%   $251.4184   $251.42   $251.40   $251.40  
  7 purchase totals = $957.79       $1,026.8912   $1,026.89   $1,026.85   $1,026.90