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 $138.77   11.847%   $155.2101   $155.21   $155.20   $155.20  
  Purchase #2 $180.71   9.532%   $197.9353   $197.94   $197.95   $197.90  
  Purchase #3 $48.79   9.584%   $53.466   $53.47   $53.45   $53.50  
  Purchase #4 $28.91   11.833%   $32.3309   $32.33   $32.35   $32.30  
  Purchase #5 $67.39   11.239%   $74.964   $74.96   $74.95   $75.00  
  Purchase #6 $195.91   10.272%   $216.0339   $216.03   $216.05   $216.00  
  Purchase #7 $92.33   3.183%   $95.2689   $95.27   $95.25   $95.30  
  7 purchase totals = $752.81       $825.2091   $825.21   $825.20   $825.20