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 $54.74   6.296%   $58.1864   $58.19   $58.20   $58.20  
  Purchase #2 $224.73   13.509%   $255.0888   $255.09   $255.10   $255.10  
  Purchase #3 $176.78   10.156%   $194.7338   $194.73   $194.75   $194.70  
  Purchase #4 $123.44   5.589%   $130.3391   $130.34   $130.35   $130.30  
  Purchase #5 $37.62   10.569%   $41.5961   $41.60   $41.60   $41.60  
  Purchase #6 $169.27   8.204%   $183.1569   $183.16   $183.15   $183.20  
  Purchase #7 $146.28   3.494%   $151.391   $151.39   $151.40   $151.40  
  7 purchase totals = $932.86       $1,014.4921   $1,014.50   $1,014.55   $1,014.50