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	$38.61	4.651%	$40.4058	$40.41	$40.40	$40.40
Purchase #2	$74.87	4.346%	$78.1239	$78.12	$78.10	$78.10
Purchase #3	$157.94	6.259%	$167.8255	$167.83	$167.85	$167.80
Purchase #4	$44.26	3.793%	$45.9388	$45.94	$45.95	$45.90
Purchase #5	$136.58	7.497%	$146.8194	$146.82	$146.80	$146.80
Purchase #6	$27.45	5.427%	$28.9397	$28.94	$28.95	$28.90
Purchase #7	$148.39	9.160%	$161.9825	$161.98	$162.00	$162.00
7 purchase totals =	$628.10		$670.0356	$670.04	$670.05	$669.90