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 $78.37   5.421%   $82.6184   $82.62   $82.60   $82.60  
  Purchase #2 $229.86   6.749%   $245.3733   $245.37   $245.35   $245.40  
  Purchase #3 $34.58   13.425%   $39.2224   $39.22   $39.20   $39.20  
  Purchase #4 $139.96   6.128%   $148.5367   $148.54   $148.55   $148.50  
  Purchase #5 $174.31   11.255%   $193.9286   $193.93   $193.95   $193.90  
  Purchase #6 $180.70   11.726%   $201.8889   $201.89   $201.90   $201.90  
  Purchase #7 $68.48   3.639%   $70.972   $70.97   $70.95   $71.00  
  7 purchase totals = $906.26       $982.5403   $982.54   $982.50   $982.50