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	$32.64	5.825%	$34.5413	$34.54	$34.55	$34.50
Purchase #2	$86.55	3.801%	$89.8398	$89.84	$89.85	$89.80
Purchase #3	$197.29	5.520%	$208.1804	$208.18	$208.20	$208.20
Purchase #4	$56.40	10.502%	$62.3231	$62.32	$62.30	$62.30
Purchase #5	$61.51	4.803%	$64.4643	$64.46	$64.45	$64.50
Purchase #6	$15.92	9.322%	$17.4041	$17.40	$17.40	$17.40
Purchase #7	$28.80	10.271%	$31.758	$31.76	$31.75	$31.80
7 purchase totals =	$479.11		$508.5110	$508.50	$508.50	$508.50