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	$46.76	11.662%	$52.2132	$52.21	$52.20	$52.20
Purchase #2	$123.73	4.725%	$129.5762	$129.58	$129.60	$129.60
Purchase #3	$48.70	11.561%	$54.3302	$54.33	$54.35	$54.30
Purchase #4	$112.50	4.722%	$117.8123	$117.81	$117.80	$117.80
Purchase #5	$209.73	11.321%	$233.4735	$233.47	$233.45	$233.50
Purchase #6	$6.67	11.751%	$7.4538	$7.45	$7.45	$7.50
Purchase #7	$235.79	3.751%	$244.6345	$244.63	$244.65	$244.60
7 purchase totals =	$783.88		$839.4937	$839.48	$839.50	$839.50