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 $83.63   11.809%   $93.5059   $93.51   $93.50   $93.50  
  Purchase #2 $25.43   3.513%   $26.3234   $26.32   $26.30   $26.30  
  Purchase #3 $222.74   3.130%   $229.7118   $229.71   $229.70   $229.70  
  Purchase #4 $119.57   4.430%   $124.867   $124.87   $124.85   $124.90  
  Purchase #5 $82.78   13.149%   $93.6647   $93.66   $93.65   $93.70  
  Purchase #6 $167.49   5.695%   $177.0286   $177.03   $177.05   $177.00  
  Purchase #7 $22.51   13.318%   $25.5079   $25.51   $25.50   $25.50  
  7 purchase totals = $724.15       $770.6093   $770.61   $770.55   $770.60