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	$169.92	12.197%	$190.6451	$190.65	$190.65	$190.60
Purchase #2	$99.30	12.308%	$111.5218	$111.52	$111.50	$111.50
Purchase #3	$94.57	7.351%	$101.5218	$101.52	$101.50	$101.50
Purchase #4	$102.65	8.139%	$111.0047	$111.00	$111.00	$111.00
Purchase #5	$184.74	5.222%	$194.3871	$194.39	$194.40	$194.40
Purchase #6	$175.43	4.534%	$183.384	$183.38	$183.40	$183.40
Purchase #7	$88.27	9.300%	$96.4791	$96.48	$96.50	$96.50
7 purchase totals =	$914.88		$988.9436	$988.94	$988.95	$988.90