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	$92.89	9.502%	$101.7164	$101.72	$101.70	$101.70
Purchase #2	$51.36	5.608%	$54.2403	$54.24	$54.25	$54.20
Purchase #3	$243.50	12.819%	$274.7143	$274.71	$274.70	$274.70
Purchase #4	$65.50	8.490%	$71.061	$71.06	$71.05	$71.10
Purchase #5	$92.46	7.282%	$99.1929	$99.19	$99.20	$99.20
Purchase #6	$92.49	9.114%	$100.9195	$100.92	$100.90	$100.90
Purchase #7	$142.54	13.431%	$161.6845	$161.68	$161.70	$161.70
7 purchase totals =	$780.74		$863.5289	$863.52	$863.50	$863.50