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	$30.69	8.511%	$33.302	$33.30	$33.30	$33.30
Purchase #2	$56.58	4.570%	$59.1657	$59.17	$59.15	$59.20
Purchase #3	$248.49	4.419%	$259.4708	$259.47	$259.45	$259.50
Purchase #4	$72.80	12.585%	$81.9619	$81.96	$81.95	$82.00
Purchase #5	$101.66	12.523%	$114.3909	$114.39	$114.40	$114.40
Purchase #6	$53.81	4.665%	$56.3202	$56.32	$56.30	$56.30
Purchase #7	$132.26	11.105%	$146.9475	$146.95	$146.95	$146.90
7 purchase totals =	$696.29		$751.5590	$751.56	$751.50	$751.60