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 $161.34   13.428%   $183.0047   $183.00   $183.00   $183.00  
  Purchase #2 $29.71   9.556%   $32.5491   $32.55   $32.55   $32.50  
  Purchase #3 $44.66   7.842%   $48.1622   $48.16   $48.15   $48.20  
  Purchase #4 $156.91   10.634%   $173.5958   $173.60   $173.60   $173.60  
  Purchase #5 $47.73   11.741%   $53.334   $53.33   $53.35   $53.30  
  Purchase #6 $239.49   10.483%   $264.5957   $264.60   $264.60   $264.60  
  Purchase #7 $111.68   6.202%   $118.6064   $118.61   $118.60   $118.60  
  7 purchase totals = $791.52       $873.8479   $873.85   $873.85   $873.80