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 $50.55   12.635%   $56.937   $56.94   $56.95   $56.90  
  Purchase #2 $72.93   5.278%   $76.7792   $76.78   $76.80   $76.80  
  Purchase #3 $179.37   9.322%   $196.0909   $196.09   $196.10   $196.10  
  Purchase #4 $125.48   3.545%   $129.9283   $129.93   $129.95   $129.90  
  Purchase #5 $109.31   5.376%   $115.1865   $115.19   $115.20   $115.20  
  Purchase #6 $24.36   8.198%   $26.357   $26.36   $26.35   $26.40  
  Purchase #7 $145.99   10.342%   $161.0883   $161.09   $161.10   $161.10  
  7 purchase totals = $707.99       $762.3672   $762.38   $762.45   $762.40