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 $205.78   7.644%   $221.5098   $221.51   $221.50   $221.50  
  Purchase #2 $98.72   5.505%   $104.1545   $104.15   $104.15   $104.20  
  Purchase #3 $163.95   11.602%   $182.9715   $182.97   $182.95   $183.00  
  Purchase #4 $146.43   10.592%   $161.9399   $161.94   $161.95   $161.90  
  Purchase #5 $233.68   5.288%   $246.037   $246.04   $246.05   $246.00  
  Purchase #6 $150.61   8.362%   $163.204   $163.20   $163.20   $163.20  
  Purchase #7 $231.39   6.684%   $246.8561   $246.86   $246.85   $246.90  
  7 purchase totals = $1,230.56       $1,326.6728   $1,326.67   $1,326.65   $1,326.70