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	$204.90	7.763%	$220.8064	$220.81	$220.80	$220.80
Purchase #2	$113.56	12.374%	$127.6119	$127.61	$127.60	$127.60
Purchase #3	$237.65	7.146%	$254.6325	$254.63	$254.65	$254.60
Purchase #4	$135.26	6.827%	$144.4942	$144.49	$144.50	$144.50
Purchase #5	$81.59	12.243%	$91.5791	$91.58	$91.60	$91.60
Purchase #6	$122.61	5.154%	$128.9293	$128.93	$128.95	$128.90
Purchase #7	$33.73	4.252%	$35.1642	$35.16	$35.15	$35.20
7 purchase totals =	$929.30		$1,003.2176	$1,003.21	$1,003.25	$1,003.20