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	$243.25	3.846%	$252.6054	$252.61	$252.60	$252.60
Purchase #2	$78.98	5.179%	$83.0704	$83.07	$83.05	$83.10
Purchase #3	$72.87	10.867%	$80.7888	$80.79	$80.80	$80.80
Purchase #4	$200.69	12.592%	$225.9609	$225.96	$225.95	$226.00
Purchase #5	$88.83	12.371%	$99.8192	$99.82	$99.80	$99.80
Purchase #6	$137.67	4.231%	$143.4948	$143.49	$143.50	$143.50
Purchase #7	$73.54	13.394%	$83.3899	$83.39	$83.40	$83.40
7 purchase totals =	$895.83		$969.1294	$969.13	$969.10	$969.20