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	$49.62	11.817%	$55.4836	$55.48	$55.50	$55.50
Purchase #2	$124.61	4.210%	$129.8561	$129.86	$129.85	$129.90
Purchase #3	$187.27	3.383%	$193.6053	$193.61	$193.60	$193.60
Purchase #4	$155.87	10.471%	$172.1911	$172.19	$172.20	$172.20
Purchase #5	$93.89	12.267%	$105.4075	$105.41	$105.40	$105.40
Purchase #6	$96.83	10.171%	$106.6786	$106.68	$106.70	$106.70
Purchase #7	$159.37	5.573%	$168.2517	$168.25	$168.25	$168.30
7 purchase totals =	$867.46		$931.4739	$931.48	$931.50	$931.60