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 $249.35   10.136%   $274.6241   $274.62   $274.60   $274.60  
  Purchase #2 $153.47   13.339%   $173.9414   $173.94   $173.95   $173.90  
  Purchase #3 $213.48   8.182%   $230.9469   $230.95   $230.95   $230.90  
  Purchase #4 $71.91   13.839%   $81.8616   $81.86   $81.85   $81.90  
  Purchase #5 $28.71   4.284%   $29.9399   $29.94   $29.95   $29.90  
  Purchase #6 $203.55   12.457%   $228.9062   $228.91   $228.90   $228.90  
  Purchase #7 $95.57   10.752%   $105.8457   $105.85   $105.85   $105.80  
  7 purchase totals = $1,016.04       $1,126.0658   $1,126.07   $1,126.05   $1,125.90