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 $208.61   3.154%   $215.1896   $215.19   $215.20   $215.20  
  Purchase #2 $92.78   12.232%   $104.1288   $104.13   $104.15   $104.10  
  Purchase #3 $142.45   13.224%   $161.2876   $161.29   $161.30   $161.30  
  Purchase #4 $226.37   3.161%   $233.5256   $233.53   $233.55   $233.50  
  Purchase #5 $179.61   13.247%   $203.4029   $203.40   $203.40   $203.40  
  Purchase #6 $13.59   9.112%   $14.8283   $14.83   $14.85   $14.80  
  Purchase #7 $164.51   13.519%   $186.7501   $186.75   $186.75   $186.80  
  7 purchase totals = $1,027.92       $1,119.1129   $1,119.12   $1,119.20   $1,119.10