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 $23.29   13.761%   $26.4949   $26.49   $26.50   $26.50  
  Purchase #2 $116.83   7.747%   $125.8808   $125.88   $125.90   $125.90  
  Purchase #3 $94.77   13.834%   $107.8805   $107.88   $107.90   $107.90  
  Purchase #4 $17.69   8.508%   $19.1951   $19.20   $19.20   $19.20  
  Purchase #5 $94.38   7.119%   $101.0989   $101.10   $101.10   $101.10  
  Purchase #6 $53.37   10.483%   $58.9648   $58.96   $58.95   $59.00  
  Purchase #7 $158.58   11.736%   $177.1909   $177.19   $177.20   $177.20  
  7 purchase totals = $558.91       $616.7059   $616.70   $616.75   $616.80