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	$162.55	6.562%	$173.2165	$173.22	$173.20	$173.20
Purchase #2	$103.50	13.678%	$117.6567	$117.66	$117.65	$117.70
Purchase #3	$114.75	7.428%	$123.2736	$123.27	$123.25	$123.30
Purchase #4	$139.42	11.577%	$155.5607	$155.56	$155.55	$155.60
Purchase #5	$160.98	7.111%	$172.4273	$172.43	$172.45	$172.40
Purchase #6	$201.53	13.572%	$228.8817	$228.88	$228.90	$228.90
Purchase #7	$42.94	12.228%	$48.1907	$48.19	$48.20	$48.20
7 purchase totals =	$925.67		$1,019.2072	$1,019.21	$1,019.20	$1,019.30