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	$8.99	12.366%	$10.1017	$10.10	$10.10	$10.10
Purchase #2	$193.99	13.784%	$220.7296	$220.73	$220.75	$220.70
Purchase #3	$196.33	13.233%	$222.3103	$222.31	$222.30	$222.30
Purchase #4	$20.46	9.194%	$22.3411	$22.34	$22.35	$22.30
Purchase #5	$28.32	13.483%	$32.1384	$32.14	$32.15	$32.10
Purchase #6	$220.85	13.836%	$251.4068	$251.41	$251.40	$251.40
Purchase #7	$56.95	4.255%	$59.3732	$59.37	$59.35	$59.40
7 purchase totals =	$725.89		$818.4011	$818.40	$818.40	$818.30