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	$225.96	13.333%	$256.0872	$256.09	$256.10	$256.10
Purchase #2	$18.41	13.308%	$20.86	$20.86	$20.85	$20.90
Purchase #3	$123.70	3.256%	$127.7277	$127.73	$127.75	$127.70
Purchase #4	$44.65	13.397%	$50.6318	$50.63	$50.65	$50.60
Purchase #5	$59.33	3.216%	$61.2381	$61.24	$61.25	$61.20
Purchase #6	$194.32	8.321%	$210.4894	$210.49	$210.50	$210.50
Purchase #7	$242.96	8.652%	$263.9809	$263.98	$264.00	$264.00
7 purchase totals =	$909.33		$991.0151	$991.02	$991.10	$991.00