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	$95.54	7.162%	$102.3826	$102.38	$102.40	$102.40
Purchase #2	$247.77	13.694%	$281.6996	$281.70	$281.70	$281.70
Purchase #3	$41.46	10.689%	$45.8917	$45.89	$45.90	$45.90
Purchase #4	$56.26	9.829%	$61.7898	$61.79	$61.80	$61.80
Purchase #5	$8.36	4.846%	$8.7651	$8.77	$8.75	$8.80
Purchase #6	$94.54	9.388%	$103.4154	$103.42	$103.40	$103.40
Purchase #7	$250.96	5.324%	$264.3211	$264.32	$264.30	$264.30
7 purchase totals =	$794.89		$868.2653	$868.27	$868.25	$868.30