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	$80.34	12.426%	$90.323	$90.32	$90.30	$90.30
Purchase #2	$58.70	4.262%	$61.2018	$61.20	$61.20	$61.20
Purchase #3	$15.62	4.500%	$16.3229	$16.32	$16.30	$16.30
Purchase #4	$54.32	12.418%	$61.0655	$61.07	$61.05	$61.10
Purchase #5	$165.35	3.821%	$171.668	$171.67	$171.65	$171.70
Purchase #6	$152.29	9.368%	$166.5565	$166.56	$166.55	$166.60
Purchase #7	$142.58	4.134%	$148.4743	$148.47	$148.45	$148.50
7 purchase totals =	$669.20		$715.6120	$715.61	$715.50	$715.70