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	$39.54	6.280%	$42.0231	$42.02	$42.00	$42.00
Purchase #2	$211.35	5.766%	$223.5364	$223.54	$223.55	$223.50
Purchase #3	$72.94	7.290%	$78.2573	$78.26	$78.25	$78.30
Purchase #4	$137.50	11.326%	$153.0733	$153.07	$153.05	$153.10
Purchase #5	$131.85	6.663%	$140.6352	$140.64	$140.65	$140.60
Purchase #6	$222.91	4.618%	$233.204	$233.20	$233.20	$233.20
Purchase #7	$65.92	8.407%	$71.4619	$71.46	$71.45	$71.50
7 purchase totals =	$882.01		$942.1912	$942.19	$942.15	$942.20