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	$43.48	4.648%	$45.501	$45.50	$45.50	$45.50
Purchase #2	$203.74	6.128%	$216.2252	$216.23	$216.25	$216.20
Purchase #3	$143.41	10.465%	$158.4179	$158.42	$158.40	$158.40
Purchase #4	$28.30	8.865%	$30.8088	$30.81	$30.80	$30.80
Purchase #5	$190.63	13.130%	$215.6597	$215.66	$215.65	$215.70
Purchase #6	$145.69	9.830%	$160.0113	$160.01	$160.00	$160.00
Purchase #7	$33.76	13.745%	$38.4003	$38.40	$38.40	$38.40
7 purchase totals =	$789.01		$865.0242	$865.03	$865.00	$865.00