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 $250.60   6.532%   $266.9692   $266.97   $266.95   $267.00  
  Purchase #2 $21.94   7.425%   $23.569   $23.57   $23.55   $23.60  
  Purchase #3 $160.46   9.279%   $175.3491   $175.35   $175.35   $175.30  
  Purchase #4 $179.49   13.868%   $204.3817   $204.38   $204.40   $204.40  
  Purchase #5 $161.81   13.788%   $184.1204   $184.12   $184.10   $184.10  
  Purchase #6 $233.57   3.768%   $242.3709   $242.37   $242.35   $242.40  
  Purchase #7 $208.83   12.104%   $234.1068   $234.11   $234.10   $234.10  
  7 purchase totals = $1,216.70       $1,330.8671   $1,330.87   $1,330.80   $1,330.90