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 $202.46   11.541%   $225.8259   $225.83   $225.85   $225.80  
  Purchase #2 $40.69   13.357%   $46.125   $46.13   $46.15   $46.10  
  Purchase #3 $166.88   5.624%   $176.2653   $176.27   $176.25   $176.30  
  Purchase #4 $58.98   12.234%   $66.1956   $66.20   $66.20   $66.20  
  Purchase #5 $182.25   5.856%   $192.9226   $192.92   $192.90   $192.90  
  Purchase #6 $221.62   5.744%   $234.3499   $234.35   $234.35   $234.30  
  Purchase #7 $13.29   6.142%   $14.1063   $14.11   $14.10   $14.10  
  7 purchase totals = $886.17       $955.7906   $955.81   $955.80   $955.70