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	$147.86	5.238%	$155.6049	$155.60	$155.60	$155.60
Purchase #2	$145.25	10.772%	$160.8963	$160.90	$160.90	$160.90
Purchase #3	$249.41	11.241%	$277.4462	$277.45	$277.45	$277.40
Purchase #4	$163.56	5.705%	$172.8911	$172.89	$172.90	$172.90
Purchase #5	$146.32	13.398%	$165.924	$165.92	$165.90	$165.90
Purchase #6	$182.33	8.406%	$197.6567	$197.66	$197.65	$197.70
Purchase #7	$17.38	13.808%	$19.7798	$19.78	$19.80	$19.80
7 purchase totals =	$1,052.11		$1,150.1990	$1,150.20	$1,150.20	$1,150.20