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	$85.79	12.855%	$96.8183	$96.82	$96.80	$96.80
Purchase #2	$235.38	8.444%	$255.2555	$255.26	$255.25	$255.30
Purchase #3	$207.63	7.330%	$222.8493	$222.85	$222.85	$222.80
Purchase #4	$48.95	12.248%	$54.9454	$54.95	$54.95	$54.90
Purchase #5	$31.63	8.794%	$34.4115	$34.41	$34.40	$34.40
Purchase #6	$152.50	8.627%	$165.6562	$165.66	$165.65	$165.70
Purchase #7	$199.36	10.563%	$220.4184	$220.42	$220.40	$220.40
7 purchase totals =	$961.24		$1,050.3546	$1,050.37	$1,050.30	$1,050.30