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	$233.47	10.624%	$258.2739	$258.27	$258.25	$258.30
Purchase #2	$46.67	13.281%	$52.8682	$52.87	$52.85	$52.90
Purchase #3	$131.54	12.741%	$148.2995	$148.30	$148.30	$148.30
Purchase #4	$21.52	5.378%	$22.6773	$22.68	$22.70	$22.70
Purchase #5	$53.94	9.531%	$59.081	$59.08	$59.10	$59.10
Purchase #6	$232.83	8.769%	$253.2469	$253.25	$253.25	$253.20
Purchase #7	$137.49	3.599%	$142.4383	$142.44	$142.45	$142.40
7 purchase totals =	$857.46		$936.8851	$936.89	$936.90	$936.90