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 $60.84   5.122%   $63.9562   $63.96   $63.95   $64.00  
  Purchase #2 $107.56   7.824%   $115.9755   $115.98   $116.00   $116.00  
  Purchase #3 $86.68   9.408%   $94.8349   $94.83   $94.85   $94.80  
  Purchase #4 $103.71   8.565%   $112.5928   $112.59   $112.60   $112.60  
  Purchase #5 $248.83   12.453%   $279.8168   $279.82   $279.80   $279.80  
  Purchase #6 $233.57   10.119%   $257.2049   $257.20   $257.20   $257.20  
  Purchase #7 $239.56   9.226%   $261.6618   $261.66   $261.65   $261.70  
  7 purchase totals = $1,080.75       $1,186.0429   $1,186.04   $1,186.05   $1,186.10