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	$150.96	10.564%	$166.9074	$166.91	$166.90	$166.90
Purchase #2	$67.27	4.651%	$70.3987	$70.40	$70.40	$70.40
Purchase #3	$250.45	5.537%	$264.3174	$264.32	$264.30	$264.30
Purchase #4	$238.94	3.680%	$247.733	$247.73	$247.75	$247.70
Purchase #5	$35.66	9.182%	$38.9343	$38.93	$38.95	$38.90
Purchase #6	$39.64	4.732%	$41.5158	$41.52	$41.50	$41.50
Purchase #7	$157.60	5.812%	$166.7597	$166.76	$166.75	$166.80
7 purchase totals =	$940.52		$996.5663	$996.57	$996.55	$996.50