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 $62.73   5.211%   $65.9989   $66.00   $66.00   $66.00  
  Purchase #2 $213.28   9.158%   $232.8122   $232.81   $232.80   $232.80  
  Purchase #3 $29.84   12.433%   $33.55   $33.55   $33.55   $33.60  
  Purchase #4 $23.91   4.300%   $24.9381   $24.94   $24.95   $24.90  
  Purchase #5 $227.30   7.557%   $244.4771   $244.48   $244.50   $244.50  
  Purchase #6 $127.60   7.545%   $137.2274   $137.23   $137.25   $137.20  
  Purchase #7 $244.66   13.269%   $277.1239   $277.12   $277.10   $277.10  
  7 purchase totals = $929.32       $1,016.1276   $1,016.13   $1,016.15   $1,016.10