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	$152.85	11.830%	$170.9322	$170.93	$170.95	$170.90
Purchase #2	$138.50	11.388%	$154.2724	$154.27	$154.25	$154.30
Purchase #3	$51.50	8.324%	$55.7869	$55.79	$55.80	$55.80
Purchase #4	$42.80	5.355%	$45.0919	$45.09	$45.10	$45.10
Purchase #5	$238.88	10.807%	$264.6958	$264.70	$264.70	$264.70
Purchase #6	$30.68	8.632%	$33.3283	$33.33	$33.35	$33.30
Purchase #7	$76.85	7.383%	$82.5238	$82.52	$82.50	$82.50
7 purchase totals =	$732.06		$806.6313	$806.63	$806.65	$806.60