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	$33.38	6.704%	$35.6178	$35.62	$35.60	$35.60
Purchase #2	$160.65	4.287%	$167.5371	$167.54	$167.55	$167.50
Purchase #3	$12.34	4.443%	$12.8883	$12.89	$12.90	$12.90
Purchase #4	$99.40	5.746%	$105.1115	$105.11	$105.10	$105.10
Purchase #5	$180.63	13.408%	$204.8489	$204.85	$204.85	$204.80
Purchase #6	$36.47	3.257%	$37.6578	$37.66	$37.65	$37.70
Purchase #7	$239.25	12.464%	$269.0701	$269.07	$269.05	$269.10
7 purchase totals =	$762.12		$832.7315	$832.74	$832.70	$832.70