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	$226.56	12.323%	$254.479	$254.48	$254.50	$254.50
Purchase #2	$140.45	12.527%	$158.0442	$158.04	$158.05	$158.00
Purchase #3	$214.41	12.200%	$240.568	$240.57	$240.55	$240.60
Purchase #4	$173.38	10.362%	$191.3456	$191.35	$191.35	$191.30
Purchase #5	$39.45	13.144%	$44.6353	$44.64	$44.65	$44.60
Purchase #6	$193.37	9.612%	$211.9567	$211.96	$211.95	$212.00
Purchase #7	$93.35	6.121%	$99.064	$99.06	$99.05	$99.10
7 purchase totals =	$1,080.97		$1,200.0928	$1,200.10	$1,200.10	$1,200.10