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	$169.88	5.566%	$179.3355	$179.34	$179.35	$179.30
Purchase #2	$250.73	9.742%	$275.1561	$275.16	$275.15	$275.20
Purchase #3	$228.31	5.657%	$241.2255	$241.23	$241.25	$241.20
Purchase #4	$57.38	3.233%	$59.2351	$59.24	$59.25	$59.20
Purchase #5	$57.30	4.114%	$59.6573	$59.66	$59.65	$59.70
Purchase #6	$27.78	3.304%	$28.6979	$28.70	$28.70	$28.70
Purchase #7	$204.97	8.789%	$222.9848	$222.98	$223.00	$223.00
7 purchase totals =	$996.35		$1,066.2922	$1,066.31	$1,066.35	$1,066.30