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 $14.67   10.603%   $16.2255   $16.23   $16.25   $16.20  
  Purchase #2 $165.62   4.209%   $172.5909   $172.59   $172.60   $172.60  
  Purchase #3 $236.37   8.166%   $255.672   $255.67   $255.65   $255.70  
  Purchase #4 $125.44   13.800%   $142.7507   $142.75   $142.75   $142.80  
  Purchase #5 $14.46   12.186%   $16.2221   $16.22   $16.20   $16.20  
  Purchase #6 $231.36   7.596%   $248.9341   $248.93   $248.95   $248.90  
  Purchase #7 $134.78   8.485%   $146.2161   $146.22   $146.20   $146.20  
  7 purchase totals = $922.70       $998.6114   $998.61   $998.60   $998.60