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	$143.57	13.532%	$162.9979	$163.00	$163.00	$163.00
Purchase #2	$88.72	3.840%	$92.1268	$92.13	$92.15	$92.10
Purchase #3	$78.31	12.503%	$88.1011	$88.10	$88.10	$88.10
Purchase #4	$243.30	6.802%	$259.8493	$259.85	$259.85	$259.80
Purchase #5	$131.27	9.850%	$144.2001	$144.20	$144.20	$144.20
Purchase #6	$162.41	10.749%	$179.8675	$179.87	$179.85	$179.90
Purchase #7	$19.31	7.563%	$20.7704	$20.77	$20.75	$20.80
7 purchase totals =	$866.89		$947.9131	$947.92	$947.90	$947.90