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 $76.72   12.532%   $86.3346   $86.33   $86.35   $86.30  
  Purchase #2 $62.75   9.665%   $68.8148   $68.81   $68.80   $68.80  
  Purchase #3 $249.65   10.417%   $275.656   $275.66   $275.65   $275.70  
  Purchase #4 $20.42   3.858%   $21.2078   $21.21   $21.20   $21.20  
  Purchase #5 $63.59   5.291%   $66.9545   $66.95   $66.95   $67.00  
  Purchase #6 $69.82   13.403%   $79.178   $79.18   $79.20   $79.20  
  Purchase #7 $242.37   13.670%   $275.502   $275.50   $275.50   $275.50  
  7 purchase totals = $785.32       $873.6477   $873.64   $873.65   $873.70