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	$29.49	10.284%	$32.5228	$32.52	$32.50	$32.50
Purchase #2	$231.67	11.776%	$258.9515	$258.95	$258.95	$259.00
Purchase #3	$154.54	9.248%	$168.8319	$168.83	$168.85	$168.80
Purchase #4	$30.74	6.153%	$32.6314	$32.63	$32.65	$32.60
Purchase #5	$226.50	9.186%	$247.3063	$247.31	$247.30	$247.30
Purchase #6	$234.29	6.154%	$248.7082	$248.71	$248.70	$248.70
Purchase #7	$142.77	9.622%	$156.5073	$156.51	$156.50	$156.50
7 purchase totals =	$1,050.00		$1,145.4594	$1,145.46	$1,145.45	$1,145.40