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	$174.83	8.617%	$189.8951	$189.90	$189.90	$189.90
Purchase #2	$33.43	10.130%	$36.8165	$36.82	$36.80	$36.80
Purchase #3	$164.66	6.575%	$175.4864	$175.49	$175.50	$175.50
Purchase #4	$74.70	5.410%	$78.7413	$78.74	$78.75	$78.70
Purchase #5	$57.84	6.308%	$61.4885	$61.49	$61.50	$61.50
Purchase #6	$97.35	6.375%	$103.5561	$103.56	$103.55	$103.60
Purchase #7	$36.97	3.645%	$38.3176	$38.32	$38.30	$38.30
7 purchase totals =	$639.78		$684.3015	$684.32	$684.30	$684.30