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 $49.86   13.510%   $56.5961   $56.60   $56.60   $56.60  
  Purchase #2 $198.55   8.291%   $215.0118   $215.01   $215.00   $215.00  
  Purchase #3 $116.58   6.692%   $124.3815   $124.38   $124.40   $124.40  
  Purchase #4 $97.50   3.800%   $101.205   $101.21   $101.20   $101.20  
  Purchase #5 $221.55   8.400%   $240.1602   $240.16   $240.15   $240.20  
  Purchase #6 $92.58   4.290%   $96.5517   $96.55   $96.55   $96.60  
  Purchase #7 $203.88   12.469%   $229.3018   $229.30   $229.30   $229.30  
  7 purchase totals = $980.50       $1,063.2081   $1,063.21   $1,063.20   $1,063.30