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 $60.72   13.726%   $69.0544   $69.05   $69.05   $69.10  
  Purchase #2 $228.42   6.646%   $243.6008   $243.60   $243.60   $243.60  
  Purchase #3 $46.29   3.742%   $48.0222   $48.02   $48.00   $48.00  
  Purchase #4 $39.58   7.310%   $42.4733   $42.47   $42.45   $42.50  
  Purchase #5 $138.76   6.521%   $147.8085   $147.81   $147.80   $147.80  
  Purchase #6 $92.91   9.647%   $101.873   $101.87   $101.85   $101.90  
  Purchase #7 $11.41   10.852%   $12.6482   $12.65   $12.65   $12.60  
  7 purchase totals = $618.09       $665.4804   $665.47   $665.40   $665.50