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	$148.82	11.803%	$166.3852	$166.39	$166.40	$166.40
Purchase #2	$123.44	10.557%	$136.4716	$136.47	$136.45	$136.50
Purchase #3	$70.58	13.714%	$80.2593	$80.26	$80.25	$80.30
Purchase #4	$175.67	7.115%	$188.1689	$188.17	$188.15	$188.20
Purchase #5	$146.36	7.643%	$157.5463	$157.55	$157.55	$157.50
Purchase #6	$52.78	13.161%	$59.7264	$59.73	$59.75	$59.70
Purchase #7	$114.86	7.797%	$123.8156	$123.82	$123.80	$123.80
7 purchase totals =	$832.51		$912.3733	$912.39	$912.35	$912.40