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	$250.26	5.846%	$264.8902	$264.89	$264.90	$264.90
Purchase #2	$29.60	9.466%	$32.4019	$32.40	$32.40	$32.40
Purchase #3	$229.38	4.713%	$240.1907	$240.19	$240.20	$240.20
Purchase #4	$219.97	12.395%	$247.2353	$247.24	$247.25	$247.20
Purchase #5	$74.65	5.571%	$78.8088	$78.81	$78.80	$78.80
Purchase #6	$222.38	3.150%	$229.385	$229.39	$229.40	$229.40
Purchase #7	$156.96	13.555%	$178.2359	$178.24	$178.25	$178.20
7 purchase totals =	$1,183.20		$1,271.1478	$1,271.16	$1,271.20	$1,271.10