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	$88.27	13.427%	$100.122	$100.12	$100.10	$100.10
Purchase #2	$56.69	6.484%	$60.3658	$60.37	$60.35	$60.40
Purchase #3	$99.95	5.483%	$105.4303	$105.43	$105.45	$105.40
Purchase #4	$188.52	3.740%	$195.5706	$195.57	$195.55	$195.60
Purchase #5	$246.80	8.435%	$267.6176	$267.62	$267.60	$267.60
Purchase #6	$155.80	4.176%	$162.3062	$162.31	$162.30	$162.30
Purchase #7	$29.70	9.474%	$32.5138	$32.51	$32.50	$32.50
7 purchase totals =	$865.73		$923.9263	$923.93	$923.85	$923.90