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 $239.95   10.266%   $264.5833   $264.58   $264.60   $264.60  
  Purchase #2 $245.45   13.810%   $279.3466   $279.35   $279.35   $279.30  
  Purchase #3 $247.44   9.789%   $271.6619   $271.66   $271.65   $271.70  
  Purchase #4 $120.65   3.308%   $124.6411   $124.64   $124.65   $124.60  
  Purchase #5 $88.35   3.486%   $91.4299   $91.43   $91.45   $91.40  
  Purchase #6 $55.33   5.795%   $58.5364   $58.54   $58.55   $58.50  
  Purchase #7 $198.92   11.275%   $221.3482   $221.35   $221.35   $221.30  
  7 purchase totals = $1,196.09       $1,311.5474   $1,311.55   $1,311.60   $1,311.40