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	$213.73	11.717%	$238.7727	$238.77	$238.75	$238.80
Purchase #2	$243.88	4.269%	$254.2912	$254.29	$254.30	$254.30
Purchase #3	$72.83	11.142%	$80.9447	$80.94	$80.95	$80.90
Purchase #4	$89.50	12.429%	$100.624	$100.62	$100.60	$100.60
Purchase #5	$34.26	12.110%	$38.4089	$38.41	$38.40	$38.40
Purchase #6	$28.80	5.409%	$30.3578	$30.36	$30.35	$30.40
Purchase #7	$213.54	9.273%	$233.3416	$233.34	$233.35	$233.30
7 purchase totals =	$896.54		$976.7409	$976.73	$976.70	$976.70