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	$63.72	12.830%	$71.8953	$71.90	$71.90	$71.90
Purchase #2	$176.30	10.142%	$194.1803	$194.18	$194.20	$194.20
Purchase #3	$90.65	10.409%	$100.0858	$100.09	$100.10	$100.10
Purchase #4	$118.61	11.533%	$132.2893	$132.29	$132.30	$132.30
Purchase #5	$72.30	6.335%	$76.8802	$76.88	$76.90	$76.90
Purchase #6	$199.76	9.549%	$218.8351	$218.84	$218.85	$218.80
Purchase #7	$91.89	11.844%	$102.7735	$102.77	$102.75	$102.80
7 purchase totals =	$813.23		$896.9395	$896.95	$897.00	$897.00