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 $236.97   12.829%   $267.3709   $267.37   $267.35   $267.40  
  Purchase #2 $104.72   11.243%   $116.4937   $116.49   $116.50   $116.50  
  Purchase #3 $233.92   13.671%   $265.8992   $265.90   $265.90   $265.90  
  Purchase #4 $18.33   6.742%   $19.5658   $19.57   $19.55   $19.60  
  Purchase #5 $170.37   13.817%   $193.91   $193.91   $193.90   $193.90  
  Purchase #6 $167.42   3.861%   $173.8841   $173.88   $173.90   $173.90  
  Purchase #7 $17.34   3.375%   $17.9252   $17.93   $17.95   $17.90  
  7 purchase totals = $949.07       $1,055.0489   $1,055.05   $1,055.05   $1,055.10