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 $54.92   12.689%   $61.8888   $61.89   $61.90   $61.90  
  Purchase #2 $42.69   4.561%   $44.6371   $44.64   $44.65   $44.60  
  Purchase #3 $162.36   12.327%   $182.3741   $182.37   $182.35   $182.40  
  Purchase #4 $141.74   9.226%   $154.8169   $154.82   $154.80   $154.80  
  Purchase #5 $186.47   13.447%   $211.5446   $211.54   $211.55   $211.50  
  Purchase #6 $85.88   10.852%   $95.1997   $95.20   $95.20   $95.20  
  Purchase #7 $22.35   5.315%   $23.5379   $23.54   $23.55   $23.50  
  7 purchase totals = $696.41       $773.9991   $774.00   $774.00   $773.90