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	$232.26	11.710%	$259.4576	$259.46	$259.45	$259.50
Purchase #2	$86.72	4.470%	$90.5964	$90.60	$90.60	$90.60
Purchase #3	$194.50	10.251%	$214.4382	$214.44	$214.45	$214.40
Purchase #4	$132.63	11.549%	$147.9474	$147.95	$147.95	$147.90
Purchase #5	$95.47	13.567%	$108.4224	$108.42	$108.40	$108.40
Purchase #6	$135.71	13.395%	$153.8884	$153.89	$153.90	$153.90
Purchase #7	$152.89	10.538%	$169.0015	$169.00	$169.00	$169.00
7 purchase totals =	$1,030.18		$1,143.7519	$1,143.76	$1,143.75	$1,143.70