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	$112.48	9.503%	$123.169	$123.17	$123.15	$123.20
Purchase #2	$78.84	4.204%	$82.1544	$82.15	$82.15	$82.20
Purchase #3	$25.32	12.219%	$28.4139	$28.41	$28.40	$28.40
Purchase #4	$48.51	9.564%	$53.1495	$53.15	$53.15	$53.10
Purchase #5	$188.84	6.457%	$201.0334	$201.03	$201.05	$201.00
Purchase #6	$25.39	10.689%	$28.1039	$28.10	$28.10	$28.10
Purchase #7	$79.42	7.565%	$85.4281	$85.43	$85.45	$85.40
7 purchase totals =	$558.80		$601.4522	$601.44	$601.45	$601.40