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	$242.89	6.176%	$257.8909	$257.89	$257.90	$257.90
Purchase #2	$108.91	6.738%	$116.2484	$116.25	$116.25	$116.20
Purchase #3	$106.82	12.445%	$120.1137	$120.11	$120.10	$120.10
Purchase #4	$214.85	13.551%	$243.9643	$243.96	$243.95	$244.00
Purchase #5	$142.34	7.279%	$152.7009	$152.70	$152.70	$152.70
Purchase #6	$183.96	13.847%	$209.4329	$209.43	$209.45	$209.40
Purchase #7	$85.71	12.566%	$96.4803	$96.48	$96.50	$96.50
7 purchase totals =	$1,085.48		$1,196.8314	$1,196.82	$1,196.85	$1,196.80