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 $192.70   6.742%   $205.6918   $205.69   $205.70   $205.70  
  Purchase #2 $104.58   10.566%   $115.6299   $115.63   $115.65   $115.60  
  Purchase #3 $234.61   11.289%   $261.0951   $261.10   $261.10   $261.10  
  Purchase #4 $59.51   7.565%   $64.0119   $64.01   $64.00   $64.00  
  Purchase #5 $183.84   6.168%   $195.1793   $195.18   $195.20   $195.20  
  Purchase #6 $103.98   12.623%   $117.1054   $117.11   $117.10   $117.10  
  Purchase #7 $116.89   10.543%   $129.2137   $129.21   $129.20   $129.20  
  7 purchase totals = $996.11       $1,087.9271   $1,087.93   $1,087.95   $1,087.90