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 $245.32   8.682%   $266.6187   $266.62   $266.60   $266.60  
  Purchase #2 $248.43   10.412%   $274.2965   $274.30   $274.30   $274.30  
  Purchase #3 $206.73   5.261%   $217.6061   $217.61   $217.60   $217.60  
  Purchase #4 $58.40   7.619%   $62.8495   $62.85   $62.85   $62.80  
  Purchase #5 $136.55   5.543%   $144.119   $144.12   $144.10   $144.10  
  Purchase #6 $185.93   11.286%   $206.9141   $206.91   $206.90   $206.90  
  Purchase #7 $104.66   8.454%   $113.508   $113.51   $113.50   $113.50  
  7 purchase totals = $1,186.02       $1,285.9119   $1,285.92   $1,285.85   $1,285.80