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	$83.68	7.310%	$89.797	$89.80	$89.80	$89.80
Purchase #2	$84.83	9.564%	$92.9431	$92.94	$92.95	$92.90
Purchase #3	$36.98	12.819%	$41.7205	$41.72	$41.70	$41.70
Purchase #4	$143.63	12.185%	$161.1313	$161.13	$161.15	$161.10
Purchase #5	$104.40	7.195%	$111.9116	$111.91	$111.90	$111.90
Purchase #6	$6.37	4.144%	$6.634	$6.63	$6.65	$6.60
Purchase #7	$205.98	8.474%	$223.4347	$223.43	$223.45	$223.40
7 purchase totals =	$665.87		$727.5722	$727.56	$727.60	$727.40