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	$146.32	9.204%	$159.7873	$159.79	$159.80	$159.80
Purchase #2	$176.77	3.195%	$182.4178	$182.42	$182.40	$182.40
Purchase #3	$100.81	13.487%	$114.4062	$114.41	$114.40	$114.40
Purchase #4	$153.88	11.149%	$171.0361	$171.04	$171.05	$171.00
Purchase #5	$142.64	12.173%	$160.0036	$160.00	$160.00	$160.00
Purchase #6	$168.73	6.293%	$179.3482	$179.35	$179.35	$179.30
Purchase #7	$51.42	4.790%	$53.883	$53.88	$53.90	$53.90
7 purchase totals =	$940.57		$1,020.8822	$1,020.89	$1,020.90	$1,020.80