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	$6.89	9.427%	$7.5395	$7.54	$7.55	$7.50
Purchase #2	$174.85	9.307%	$191.1233	$191.12	$191.10	$191.10
Purchase #3	$90.28	4.594%	$94.4275	$94.43	$94.45	$94.40
Purchase #4	$48.47	12.818%	$54.6829	$54.68	$54.70	$54.70
Purchase #5	$186.41	7.560%	$200.5026	$200.50	$200.50	$200.50
Purchase #6	$31.96	4.871%	$33.5168	$33.52	$33.50	$33.50
Purchase #7	$174.30	13.198%	$197.3041	$197.30	$197.30	$197.30
7 purchase totals =	$713.16		$779.0967	$779.09	$779.10	$779.00