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	$169.91	3.108%	$175.1908	$175.19	$175.20	$175.20
Purchase #2	$186.90	6.185%	$198.4598	$198.46	$198.45	$198.50
Purchase #3	$155.69	10.780%	$172.4734	$172.47	$172.45	$172.50
Purchase #4	$201.73	13.226%	$228.4108	$228.41	$228.40	$228.40
Purchase #5	$127.28	4.178%	$132.5978	$132.60	$132.60	$132.60
Purchase #6	$99.80	10.141%	$109.9207	$109.92	$109.90	$109.90
Purchase #7	$178.58	9.826%	$196.1273	$196.13	$196.15	$196.10
7 purchase totals =	$1,119.89		$1,213.1806	$1,213.18	$1,213.15	$1,213.20