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	$100.34	3.286%	$103.6372	$103.64	$103.65	$103.60
Purchase #2	$230.89	10.231%	$254.5124	$254.51	$254.50	$254.50
Purchase #3	$144.73	8.600%	$157.1768	$157.18	$157.20	$157.20
Purchase #4	$61.28	11.860%	$68.5478	$68.55	$68.55	$68.50
Purchase #5	$72.41	13.562%	$82.2302	$82.23	$82.25	$82.20
Purchase #6	$67.95	10.478%	$75.0698	$75.07	$75.05	$75.10
Purchase #7	$56.89	3.846%	$59.078	$59.08	$59.10	$59.10
7 purchase totals =	$734.49		$800.2522	$800.26	$800.30	$800.20