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	$94.25	12.749%	$106.2659	$106.27	$106.25	$106.30
Purchase #2	$111.89	10.336%	$123.455	$123.46	$123.45	$123.50
Purchase #3	$113.41	5.814%	$120.0037	$120.00	$120.00	$120.00
Purchase #4	$71.25	6.699%	$76.023	$76.02	$76.00	$76.00
Purchase #5	$39.81	8.615%	$43.2396	$43.24	$43.25	$43.20
Purchase #6	$231.89	12.222%	$260.2316	$260.23	$260.25	$260.20
Purchase #7	$6.83	8.627%	$7.4192	$7.42	$7.40	$7.40
7 purchase totals =	$669.33		$736.6380	$736.64	$736.60	$736.60