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	$137.27	13.789%	$156.1982	$156.20	$156.20	$156.20
Purchase #2	$22.94	6.464%	$24.4228	$24.42	$24.40	$24.40
Purchase #3	$222.30	4.263%	$231.7766	$231.78	$231.80	$231.80
Purchase #4	$28.76	12.632%	$32.393	$32.39	$32.40	$32.40
Purchase #5	$70.63	13.833%	$80.4002	$80.40	$80.40	$80.40
Purchase #6	$162.53	6.838%	$173.6438	$173.64	$173.65	$173.60
Purchase #7	$151.34	5.495%	$159.6561	$159.66	$159.65	$159.70
7 purchase totals =	$795.77		$858.4907	$858.49	$858.50	$858.50