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 $115.43   8.292%   $125.0015   $125.00   $125.00   $125.00  
  Purchase #2 $125.32   13.474%   $142.2056   $142.21   $142.20   $142.20  
  Purchase #3 $12.76   10.497%   $14.0994   $14.10   $14.10   $14.10  
  Purchase #4 $124.65   4.776%   $130.6033   $130.60   $130.60   $130.60  
  Purchase #5 $61.76   7.135%   $66.1666   $66.17   $66.15   $66.20  
  Purchase #6 $75.93   6.707%   $81.0226   $81.02   $81.00   $81.00  
  Purchase #7 $205.31   8.111%   $221.9627   $221.96   $221.95   $222.00  
  7 purchase totals = $721.16       $781.0617   $781.06   $781.00   $781.10