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 $217.62   13.307%   $246.5787   $246.58   $246.60   $246.60  
  Purchase #2 $172.93   11.359%   $192.5731   $192.57   $192.55   $192.60  
  Purchase #3 $79.38   8.257%   $85.9344   $85.93   $85.95   $85.90  
  Purchase #4 $238.35   9.506%   $261.0076   $261.01   $261.00   $261.00  
  Purchase #5 $195.45   4.563%   $204.3684   $204.37   $204.35   $204.40  
  Purchase #6 $245.45   4.654%   $256.8732   $256.87   $256.85   $256.90  
  Purchase #7 $92.76   13.555%   $105.3336   $105.33   $105.35   $105.30  
  7 purchase totals = $1,241.94       $1,352.6690   $1,352.66   $1,352.65   $1,352.70