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	$149.37	10.554%	$165.1345	$165.13	$165.15	$165.10
Purchase #2	$91.92	7.861%	$99.1458	$99.15	$99.15	$99.10
Purchase #3	$36.65	11.560%	$40.8867	$40.89	$40.90	$40.90
Purchase #4	$133.94	4.463%	$139.9177	$139.92	$139.90	$139.90
Purchase #5	$33.92	3.232%	$35.0163	$35.02	$35.00	$35.00
Purchase #6	$144.63	9.555%	$158.4494	$158.45	$158.45	$158.40
Purchase #7	$63.73	9.598%	$69.8468	$69.85	$69.85	$69.80
7 purchase totals =	$654.16		$708.3972	$708.41	$708.40	$708.20