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 $167.64   9.753%   $183.9899   $183.99   $184.00   $184.00  
  Purchase #2 $156.72   13.704%   $178.1969   $178.20   $178.20   $178.20  
  Purchase #3 $203.64   12.574%   $229.2457   $229.25   $229.25   $229.20  
  Purchase #4 $239.37   5.550%   $252.655   $252.66   $252.65   $252.70  
  Purchase #5 $39.85   7.606%   $42.881   $42.88   $42.90   $42.90  
  Purchase #6 $14.73   3.608%   $15.2615   $15.26   $15.25   $15.30  
  Purchase #7 $54.35   9.726%   $59.6361   $59.64   $59.65   $59.60  
  7 purchase totals = $876.30       $961.8661   $961.88   $961.90   $961.90