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 $226.82   11.784%   $253.5485   $253.55   $253.55   $253.50  
  Purchase #2 $153.42   13.637%   $174.3419   $174.34   $174.35   $174.30  
  Purchase #3 $104.96   9.265%   $114.6845   $114.68   $114.70   $114.70  
  Purchase #4 $102.90   7.633%   $110.7544   $110.75   $110.75   $110.80  
  Purchase #5 $96.72   12.115%   $108.4376   $108.44   $108.45   $108.40  
  Purchase #6 $185.91   3.438%   $192.3016   $192.30   $192.30   $192.30  
  Purchase #7 $9.80   10.738%   $10.8523   $10.85   $10.85   $10.90  
  7 purchase totals = $880.53       $964.9208   $964.91   $964.95   $964.90