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	$154.33	5.694%	$163.1176	$163.12	$163.10	$163.10
Purchase #2	$41.83	9.831%	$45.9423	$45.94	$45.95	$45.90
Purchase #3	$56.85	5.704%	$60.0927	$60.09	$60.10	$60.10
Purchase #4	$58.90	3.370%	$60.8849	$60.88	$60.90	$60.90
Purchase #5	$75.28	10.107%	$82.8885	$82.89	$82.90	$82.90
Purchase #6	$94.68	5.454%	$99.8438	$99.84	$99.85	$99.80
Purchase #7	$158.56	4.346%	$165.451	$165.45	$165.45	$165.50
7 purchase totals =	$640.43		$678.2208	$678.21	$678.25	$678.20