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	$83.75	12.575%	$94.2816	$94.28	$94.30	$94.30
Purchase #2	$103.64	7.651%	$111.5695	$111.57	$111.55	$111.60
Purchase #3	$187.70	11.199%	$208.7205	$208.72	$208.70	$208.70
Purchase #4	$107.61	8.320%	$116.5632	$116.56	$116.55	$116.60
Purchase #5	$182.50	6.530%	$194.4173	$194.42	$194.40	$194.40
Purchase #6	$22.80	3.150%	$23.5182	$23.52	$23.50	$23.50
Purchase #7	$82.63	8.624%	$89.756	$89.76	$89.75	$89.80
7 purchase totals =	$770.63		$838.8263	$838.83	$838.75	$838.90