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 $236.57   13.220%   $267.8446   $267.84   $267.85   $267.80  
  Purchase #2 $142.59   12.867%   $160.9371   $160.94   $160.95   $160.90  
  Purchase #3 $125.28   9.597%   $137.3031   $137.30   $137.30   $137.30  
  Purchase #4 $98.75   9.210%   $107.8449   $107.84   $107.85   $107.80  
  Purchase #5 $206.25   4.416%   $215.358   $215.36   $215.35   $215.40  
  Purchase #6 $96.50   7.284%   $103.5291   $103.53   $103.55   $103.50  
  Purchase #7 $119.86   10.569%   $132.528   $132.53   $132.55   $132.50  
  7 purchase totals = $1,025.80       $1,125.3448   $1,125.34   $1,125.40   $1,125.20