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	$39.60	7.362%	$42.5154	$42.52	$42.50	$42.50
Purchase #2	$182.97	9.320%	$200.0228	$200.02	$200.00	$200.00
Purchase #3	$211.68	6.537%	$225.5175	$225.52	$225.50	$225.50
Purchase #4	$77.40	13.356%	$87.7375	$87.74	$87.75	$87.70
Purchase #5	$143.88	12.647%	$162.0765	$162.08	$162.10	$162.10
Purchase #6	$58.42	4.506%	$61.0524	$61.05	$61.05	$61.10
Purchase #7	$62.54	6.553%	$66.6382	$66.64	$66.65	$66.60
7 purchase totals =	$776.49		$845.5603	$845.57	$845.55	$845.50