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 $219.59   6.560%   $233.9951   $234.00   $234.00   $234.00  
  Purchase #2 $76.64   9.452%   $83.884   $83.88   $83.90   $83.90  
  Purchase #3 $76.43   3.418%   $79.0424   $79.04   $79.05   $79.00  
  Purchase #4 $247.49   8.590%   $268.7494   $268.75   $268.75   $268.70  
  Purchase #5 $58.71   9.662%   $64.3826   $64.38   $64.40   $64.40  
  Purchase #6 $14.30   6.217%   $15.189   $15.19   $15.20   $15.20  
  Purchase #7 $11.69   10.121%   $12.8731   $12.87   $12.85   $12.90  
  7 purchase totals = $704.85       $758.1156   $758.11   $758.15   $758.10