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 $218.97   5.503%   $231.0199   $231.02   $231.00   $231.00  
  Purchase #2 $139.29   10.779%   $154.3041   $154.30   $154.30   $154.30  
  Purchase #3 $217.92   6.647%   $232.4051   $232.41   $232.40   $232.40  
  Purchase #4 $175.88   9.733%   $192.9984   $193.00   $193.00   $193.00  
  Purchase #5 $24.58   5.469%   $25.9243   $25.92   $25.90   $25.90  
  Purchase #6 $42.30   11.166%   $47.0232   $47.02   $47.00   $47.00  
  Purchase #7 $119.61   10.512%   $132.1834   $132.18   $132.20   $132.20  
  7 purchase totals = $938.55       $1,015.8584   $1,015.85   $1,015.80   $1,015.80