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 $90.98   5.472%   $95.9584   $95.96   $95.95   $96.00  
  Purchase #2 $54.38   5.103%   $57.155   $57.16   $57.15   $57.20  
  Purchase #3 $24.31   6.126%   $25.7992   $25.80   $25.80   $25.80  
  Purchase #4 $199.59   3.358%   $206.2922   $206.29   $206.30   $206.30  
  Purchase #5 $166.51   11.611%   $185.8435   $185.84   $185.85   $185.80  
  Purchase #6 $145.55   12.735%   $164.0858   $164.09   $164.10   $164.10  
  Purchase #7 $221.46   9.530%   $242.5651   $242.57   $242.55   $242.60  
  7 purchase totals = $902.78       $977.6992   $977.71   $977.70   $977.80