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	$206.25	11.103%	$229.1499	$229.15	$229.15	$229.10
Purchase #2	$79.56	12.629%	$89.6076	$89.61	$89.60	$89.60
Purchase #3	$125.86	3.274%	$129.9807	$129.98	$130.00	$130.00
Purchase #4	$156.90	12.438%	$176.4152	$176.42	$176.40	$176.40
Purchase #5	$79.35	11.562%	$88.5244	$88.52	$88.50	$88.50
Purchase #6	$94.73	5.614%	$100.0481	$100.05	$100.05	$100.00
Purchase #7	$152.59	8.222%	$165.1359	$165.14	$165.15	$165.10
7 purchase totals =	$895.24		$978.8618	$978.87	$978.85	$978.70