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 $92.41   5.590%   $97.5757   $97.58   $97.60   $97.60  
  Purchase #2 $12.99   7.313%   $13.94   $13.94   $13.95   $13.90  
  Purchase #3 $185.60   4.184%   $193.3655   $193.37   $193.35   $193.40  
  Purchase #4 $85.51   3.582%   $88.573   $88.57   $88.55   $88.60  
  Purchase #5 $236.71   13.570%   $268.8315   $268.83   $268.85   $268.80  
  Purchase #6 $54.67   12.549%   $61.5305   $61.53   $61.55   $61.50  
  Purchase #7 $42.28   5.417%   $44.5703   $44.57   $44.55   $44.60  
  7 purchase totals = $710.17       $768.3865   $768.39   $768.40   $768.40