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	$37.33	7.150%	$39.9991	$40.00	$40.00	$40.00
Purchase #2	$144.95	7.545%	$155.8865	$155.89	$155.90	$155.90
Purchase #3	$127.90	6.834%	$136.6407	$136.64	$136.65	$136.60
Purchase #4	$38.31	13.530%	$43.4933	$43.49	$43.50	$43.50
Purchase #5	$85.59	11.362%	$95.3147	$95.31	$95.30	$95.30
Purchase #6	$158.78	10.702%	$175.7726	$175.77	$175.75	$175.80
Purchase #7	$178.80	6.355%	$190.1627	$190.16	$190.15	$190.20
7 purchase totals =	$771.66		$837.2696	$837.26	$837.25	$837.30