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	$240.49	13.604%	$273.2063	$273.21	$273.20	$273.20
Purchase #2	$131.88	9.410%	$144.2899	$144.29	$144.30	$144.30
Purchase #3	$91.44	10.355%	$100.9086	$100.91	$100.90	$100.90
Purchase #4	$79.31	11.259%	$88.2395	$88.24	$88.25	$88.20
Purchase #5	$160.44	4.484%	$167.6341	$167.63	$167.65	$167.60
Purchase #6	$248.87	9.245%	$271.878	$271.88	$271.90	$271.90
Purchase #7	$153.84	12.850%	$173.6084	$173.61	$173.60	$173.60
7 purchase totals =	$1,106.27		$1,219.7648	$1,219.77	$1,219.80	$1,219.70