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 $32.54   12.297%   $36.5414   $36.54   $36.55   $36.50  
  Purchase #2 $237.32   3.593%   $245.8469   $245.85   $245.85   $245.80  
  Purchase #3 $196.88   9.459%   $215.5029   $215.50   $215.50   $215.50  
  Purchase #4 $184.94   13.612%   $210.114   $210.11   $210.10   $210.10  
  Purchase #5 $218.55   8.710%   $237.5857   $237.59   $237.60   $237.60  
  Purchase #6 $226.93   12.856%   $256.1041   $256.10   $256.10   $256.10  
  Purchase #7 $195.47   11.390%   $217.734   $217.73   $217.75   $217.70  
  7 purchase totals = $1,292.63       $1,419.4290   $1,419.42   $1,419.45   $1,419.30