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 $214.36   11.461%   $238.9278   $238.93   $238.95   $238.90  
  Purchase #2 $117.69   10.778%   $130.3746   $130.37   $130.35   $130.40  
  Purchase #3 $174.77   5.533%   $184.44   $184.44   $184.45   $184.40  
  Purchase #4 $20.47   12.554%   $23.0398   $23.04   $23.05   $23.00  
  Purchase #5 $93.53   12.801%   $105.5028   $105.50   $105.50   $105.50  
  Purchase #6 $15.53   13.571%   $17.6376   $17.64   $17.65   $17.60  
  Purchase #7 $52.36   11.472%   $58.3667   $58.37   $58.35   $58.40  
  7 purchase totals = $688.71       $758.2893   $758.29   $758.30   $758.20