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 $231.87   12.684%   $261.2804   $261.28   $261.30   $261.30  
  Purchase #2 $210.53   13.103%   $238.1157   $238.12   $238.10   $238.10  
  Purchase #3 $84.28   12.239%   $94.595   $94.60   $94.60   $94.60  
  Purchase #4 $236.94   13.539%   $269.0193   $269.02   $269.00   $269.00  
  Purchase #5 $95.35   5.482%   $100.5771   $100.58   $100.60   $100.60  
  Purchase #6 $51.94   10.578%   $57.4342   $57.43   $57.45   $57.40  
  Purchase #7 $68.29   8.311%   $73.9656   $73.97   $73.95   $74.00  
  7 purchase totals = $979.20       $1,094.9873   $1,095.00   $1,095.00   $1,095.00