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 $88.66   4.491%   $92.6417   $92.64   $92.65   $92.60  
  Purchase #2 $200.87   4.551%   $210.0116   $210.01   $210.00   $210.00  
  Purchase #3 $49.80   9.777%   $54.6689   $54.67   $54.65   $54.70  
  Purchase #4 $29.73   11.307%   $33.0916   $33.09   $33.10   $33.10  
  Purchase #5 $14.77   5.328%   $15.5569   $15.56   $15.55   $15.60  
  Purchase #6 $161.42   13.284%   $182.863   $182.86   $182.85   $182.90  
  Purchase #7 $206.65   3.589%   $214.0667   $214.07   $214.05   $214.10  
  7 purchase totals = $751.90       $802.9004   $802.90   $802.85   $803.00