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	$109.27	9.842%	$120.0244	$120.02	$120.00	$120.00
Purchase #2	$235.51	6.599%	$251.0513	$251.05	$251.05	$251.10
Purchase #3	$94.29	5.437%	$99.4165	$99.42	$99.40	$99.40
Purchase #4	$127.86	7.715%	$137.7244	$137.72	$137.70	$137.70
Purchase #5	$215.37	3.208%	$222.2791	$222.28	$222.30	$222.30
Purchase #6	$173.81	13.212%	$196.7738	$196.77	$196.75	$196.80
Purchase #7	$69.28	3.394%	$71.6314	$71.63	$71.65	$71.60
7 purchase totals =	$1,025.39		$1,098.9009	$1,098.89	$1,098.85	$1,098.90