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 $32.26   9.541%   $35.3379   $35.34   $35.35   $35.30  
  Purchase #2 $124.99   5.757%   $132.1857   $132.19   $132.20   $132.20  
  Purchase #3 $218.86   6.261%   $232.5628   $232.56   $232.55   $232.60  
  Purchase #4 $115.44   9.202%   $126.0628   $126.06   $126.05   $126.10  
  Purchase #5 $61.91   4.382%   $64.6229   $64.62   $64.60   $64.60  
  Purchase #6 $157.50   4.785%   $165.0364   $165.04   $165.05   $165.00  
  Purchase #7 $114.48   8.251%   $123.9257   $123.93   $123.95   $123.90  
  7 purchase totals = $825.44       $879.7342   $879.74   $879.75   $879.70