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	$110.77	5.431%	$116.7859	$116.79	$116.80	$116.80
Purchase #2	$187.70	3.620%	$194.4947	$194.49	$194.50	$194.50
Purchase #3	$90.40	8.659%	$98.2277	$98.23	$98.25	$98.20
Purchase #4	$152.67	13.248%	$172.8957	$172.90	$172.90	$172.90
Purchase #5	$103.84	7.390%	$111.5138	$111.51	$111.50	$111.50
Purchase #6	$20.61	4.144%	$21.4641	$21.46	$21.45	$21.50
Purchase #7	$242.73	4.770%	$254.3082	$254.31	$254.30	$254.30
7 purchase totals =	$908.72		$969.6901	$969.69	$969.70	$969.70