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	$71.28	9.396%	$77.9775	$77.98	$78.00	$78.00
Purchase #2	$218.75	4.352%	$228.27	$228.27	$228.25	$228.30
Purchase #3	$170.66	8.366%	$184.9374	$184.94	$184.95	$184.90
Purchase #4	$248.96	6.300%	$264.6445	$264.64	$264.65	$264.60
Purchase #5	$104.89	4.809%	$109.9342	$109.93	$109.95	$109.90
Purchase #6	$18.67	11.409%	$20.8001	$20.80	$20.80	$20.80
Purchase #7	$126.27	4.597%	$132.0746	$132.07	$132.05	$132.10
7 purchase totals =	$959.48		$1,018.6383	$1,018.63	$1,018.65	$1,018.60