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 $234.53   11.797%   $262.1975   $262.20   $262.20   $262.20  
  Purchase #2 $38.30   6.865%   $40.9293   $40.93   $40.95   $40.90  
  Purchase #3 $66.50   3.735%   $68.9838   $68.98   $69.00   $69.00  
  Purchase #4 $159.49   3.760%   $165.4868   $165.49   $165.50   $165.50  
  Purchase #5 $143.57   10.485%   $158.6233   $158.62   $158.60   $158.60  
  Purchase #6 $58.42   13.404%   $66.2506   $66.25   $66.25   $66.30  
  Purchase #7 $169.97   8.178%   $183.8701   $183.87   $183.85   $183.90  
  7 purchase totals = $870.78       $946.3414   $946.34   $946.35   $946.40