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	$244.46	12.172%	$274.2157	$274.22	$274.20	$274.20
Purchase #2	$153.94	10.732%	$170.4608	$170.46	$170.45	$170.50
Purchase #3	$51.76	9.269%	$56.5576	$56.56	$56.55	$56.60
Purchase #4	$136.58	9.322%	$149.312	$149.31	$149.30	$149.30
Purchase #5	$117.84	5.459%	$124.2729	$124.27	$124.25	$124.30
Purchase #6	$114.59	7.412%	$123.0834	$123.08	$123.10	$123.10
Purchase #7	$202.69	9.785%	$222.5232	$222.52	$222.50	$222.50
7 purchase totals =	$1,021.86		$1,120.4256	$1,120.42	$1,120.35	$1,120.50