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 $61.32   3.658%   $63.5631   $63.56   $63.55   $63.60  
  Purchase #2 $227.46   5.763%   $240.5685   $240.57   $240.55   $240.60  
  Purchase #3 $52.83   4.581%   $55.2501   $55.25   $55.25   $55.30  
  Purchase #4 $74.62   8.509%   $80.9694   $80.97   $80.95   $81.00  
  Purchase #5 $13.66   13.509%   $15.5053   $15.51   $15.50   $15.50  
  Purchase #6 $153.72   10.257%   $169.4871   $169.49   $169.50   $169.50  
  Purchase #7 $108.51   3.481%   $112.2872   $112.29   $112.30   $112.30  
  7 purchase totals = $692.12       $737.6307   $737.64   $737.60   $737.80