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 $61.84   12.135%   $69.3443   $69.34   $69.35   $69.30  
  Purchase #2 $132.41   5.104%   $139.1682   $139.17   $139.15   $139.20  
  Purchase #3 $135.50   4.435%   $141.5094   $141.51   $141.50   $141.50  
  Purchase #4 $178.53   7.392%   $191.7269   $191.73   $191.75   $191.70  
  Purchase #5 $207.37   8.389%   $224.7663   $224.77   $224.75   $224.80  
  Purchase #6 $78.41   12.480%   $88.1956   $88.20   $88.20   $88.20  
  Purchase #7 $82.73   3.849%   $85.9143   $85.91   $85.90   $85.90  
  7 purchase totals = $876.79       $940.6250   $940.63   $940.60   $940.60