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	$52.50	11.615%	$58.5979	$58.60	$58.60	$58.60
Purchase #2	$94.57	11.465%	$105.4125	$105.41	$105.40	$105.40
Purchase #3	$30.58	10.628%	$33.83	$33.83	$33.85	$33.80
Purchase #4	$151.64	7.266%	$162.6582	$162.66	$162.65	$162.70
Purchase #5	$182.78	7.719%	$196.8888	$196.89	$196.90	$196.90
Purchase #6	$236.42	6.489%	$251.7613	$251.76	$251.75	$251.80
Purchase #7	$26.97	11.172%	$29.9831	$29.98	$30.00	$30.00
7 purchase totals =	$775.46		$839.1318	$839.13	$839.15	$839.20