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 $241.96   13.454%   $274.5133   $274.51   $274.50   $274.50  
  Purchase #2 $186.57   3.634%   $193.35   $193.35   $193.35   $193.40  
  Purchase #3 $32.39   9.565%   $35.4881   $35.49   $35.50   $35.50  
  Purchase #4 $209.54   9.634%   $229.7271   $229.73   $229.75   $229.70  
  Purchase #5 $178.49   7.730%   $192.2873   $192.29   $192.30   $192.30  
  Purchase #6 $50.36   7.712%   $54.2438   $54.24   $54.25   $54.20  
  Purchase #7 $93.45   12.764%   $105.378   $105.38   $105.40   $105.40  
  7 purchase totals = $992.76       $1,084.9876   $1,084.99   $1,085.05   $1,085.00