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	$78.76	7.671%	$84.8017	$84.80	$84.80	$84.80
Purchase #2	$53.82	13.607%	$61.1433	$61.14	$61.15	$61.10
Purchase #3	$230.85	10.600%	$255.3201	$255.32	$255.30	$255.30
Purchase #4	$84.59	5.697%	$89.4091	$89.41	$89.40	$89.40
Purchase #5	$16.81	7.362%	$18.0476	$18.05	$18.05	$18.00
Purchase #6	$49.70	12.370%	$55.8479	$55.85	$55.85	$55.80
Purchase #7	$207.32	11.360%	$230.8716	$230.87	$230.85	$230.90
7 purchase totals =	$721.85		$795.4413	$795.44	$795.40	$795.30