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 $173.28   12.486%   $194.9157   $194.92   $194.90   $194.90  
  Purchase #2 $118.95   6.155%   $126.2714   $126.27   $126.25   $126.30  
  Purchase #3 $9.51   5.818%   $10.0633   $10.06   $10.05   $10.10  
  Purchase #4 $118.50   11.366%   $131.9687   $131.97   $131.95   $132.00  
  Purchase #5 $159.36   12.783%   $179.731   $179.73   $179.75   $179.70  
  Purchase #6 $42.70   13.872%   $48.6233   $48.62   $48.60   $48.60  
  Purchase #7 $244.73   12.285%   $274.7951   $274.80   $274.80   $274.80  
  7 purchase totals = $867.03       $966.3685   $966.37   $966.30   $966.40