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	$172.77	9.126%	$188.537	$188.54	$188.55	$188.50
Purchase #2	$136.88	6.312%	$145.5199	$145.52	$145.50	$145.50
Purchase #3	$50.69	8.332%	$54.9135	$54.91	$54.90	$54.90
Purchase #4	$116.32	7.223%	$124.7218	$124.72	$124.70	$124.70
Purchase #5	$64.43	9.818%	$70.7557	$70.76	$70.75	$70.80
Purchase #6	$149.96	11.173%	$166.715	$166.72	$166.70	$166.70
Purchase #7	$162.52	4.838%	$170.3827	$170.38	$170.40	$170.40
7 purchase totals =	$853.57		$921.5456	$921.55	$921.50	$921.50