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 $48.98   13.586%   $55.6344   $55.63   $55.65   $55.60  
  Purchase #2 $6.42   13.119%   $7.2622   $7.26   $7.25   $7.30  
  Purchase #3 $54.41   11.677%   $60.7635   $60.76   $60.75   $60.80  
  Purchase #4 $206.94   6.600%   $220.598   $220.60   $220.60   $220.60  
  Purchase #5 $87.26   12.591%   $98.2469   $98.25   $98.25   $98.20  
  Purchase #6 $233.84   13.666%   $265.7966   $265.80   $265.80   $265.80  
  Purchase #7 $36.33   9.522%   $39.7893   $39.79   $39.80   $39.80  
  7 purchase totals = $674.18       $748.0909   $748.09   $748.10   $748.10