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 $175.42   5.488%   $185.047   $185.05   $185.05   $185.00  
  Purchase #2 $62.30   7.726%   $67.1133   $67.11   $67.10   $67.10  
  Purchase #3 $62.78   11.498%   $69.9984   $70.00   $70.00   $70.00  
  Purchase #4 $224.32   5.255%   $236.108   $236.11   $236.10   $236.10  
  Purchase #5 $162.40   8.365%   $175.9848   $175.98   $176.00   $176.00  
  Purchase #6 $69.91   13.525%   $79.3653   $79.37   $79.35   $79.40  
  Purchase #7 $157.66   10.555%   $174.301   $174.30   $174.30   $174.30  
  7 purchase totals = $914.79       $987.9178   $987.92   $987.90   $987.90