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	$44.42	9.328%	$48.5635	$48.56	$48.55	$48.60
Purchase #2	$115.54	10.687%	$127.8878	$127.89	$127.90	$127.90
Purchase #3	$145.57	9.228%	$159.0032	$159.00	$159.00	$159.00
Purchase #4	$50.99	8.376%	$55.2609	$55.26	$55.25	$55.30
Purchase #5	$62.34	5.284%	$65.634	$65.63	$65.65	$65.60
Purchase #6	$137.49	4.232%	$143.3086	$143.31	$143.30	$143.30
Purchase #7	$67.84	5.425%	$71.5203	$71.52	$71.50	$71.50
7 purchase totals =	$624.19		$671.1783	$671.17	$671.15	$671.20