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	$31.58	8.196%	$34.1683	$34.17	$34.15	$34.20
Purchase #2	$105.98	13.221%	$119.9916	$119.99	$120.00	$120.00
Purchase #3	$214.87	6.632%	$229.1202	$229.12	$229.10	$229.10
Purchase #4	$93.89	12.259%	$105.4	$105.40	$105.40	$105.40
Purchase #5	$55.91	6.271%	$59.4161	$59.42	$59.40	$59.40
Purchase #6	$193.54	3.248%	$199.8262	$199.83	$199.85	$199.80
Purchase #7	$127.78	13.774%	$145.3804	$145.38	$145.40	$145.40
7 purchase totals =	$823.55		$893.3028	$893.31	$893.30	$893.30