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 $52.86   10.811%   $58.5747   $58.57   $58.55   $58.60  
  Purchase #2 $129.67   3.151%   $133.7559   $133.76   $133.75   $133.80  
  Purchase #3 $109.64   3.735%   $113.7351   $113.74   $113.75   $113.70  
  Purchase #4 $213.96   4.852%   $224.3413   $224.34   $224.35   $224.30  
  Purchase #5 $162.74   3.807%   $168.9355   $168.94   $168.95   $168.90  
  Purchase #6 $81.50   7.773%   $87.835   $87.84   $87.85   $87.80  
  Purchase #7 $188.78   3.180%   $194.7832   $194.78   $194.80   $194.80  
  7 purchase totals = $939.15       $981.9607   $981.97   $982.00   $981.90