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 $232.35   3.848%   $241.2908   $241.29   $241.30   $241.30  
  Purchase #2 $140.49   11.312%   $156.3822   $156.38   $156.40   $156.40  
  Purchase #3 $196.82   13.269%   $222.936   $222.94   $222.95   $222.90  
  Purchase #4 $224.38   10.455%   $247.8389   $247.84   $247.85   $247.80  
  Purchase #5 $26.64   7.617%   $28.6692   $28.67   $28.65   $28.70  
  Purchase #6 $215.88   13.479%   $244.9785   $244.98   $245.00   $245.00  
  Purchase #7 $54.54   12.505%   $61.3602   $61.36   $61.35   $61.40  
  7 purchase totals = $1,091.10       $1,203.4558   $1,203.46   $1,203.50   $1,203.50