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 $207.94   11.548%   $231.9529   $231.95   $231.95   $232.00  
  Purchase #2 $179.71   9.578%   $196.9226   $196.92   $196.90   $196.90  
  Purchase #3 $237.61   5.480%   $250.631   $250.63   $250.65   $250.60  
  Purchase #4 $206.82   6.549%   $220.3646   $220.36   $220.35   $220.40  
  Purchase #5 $113.51   3.118%   $117.0492   $117.05   $117.05   $117.00  
  Purchase #6 $137.58   5.859%   $145.6408   $145.64   $145.65   $145.60  
  Purchase #7 $58.92   4.836%   $61.7694   $61.77   $61.75   $61.80  
  7 purchase totals = $1,142.09       $1,224.3305   $1,224.32   $1,224.30   $1,224.30