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	$176.69	7.441%	$189.8375	$189.84	$189.85	$189.80
Purchase #2	$101.38	12.613%	$114.1671	$114.17	$114.15	$114.20
Purchase #3	$230.67	10.453%	$254.7819	$254.78	$254.80	$254.80
Purchase #4	$145.31	4.874%	$152.3924	$152.39	$152.40	$152.40
Purchase #5	$99.76	10.494%	$110.2288	$110.23	$110.25	$110.20
Purchase #6	$28.94	11.218%	$32.1865	$32.19	$32.20	$32.20
Purchase #7	$224.58	3.653%	$232.7839	$232.78	$232.80	$232.80
7 purchase totals =	$1,007.33		$1,086.3781	$1,086.38	$1,086.45	$1,086.40