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	$43.97	12.747%	$49.5749	$49.57	$49.55	$49.60
Purchase #2	$117.61	4.721%	$123.1624	$123.16	$123.15	$123.20
Purchase #3	$208.64	9.319%	$228.0832	$228.08	$228.10	$228.10
Purchase #4	$32.56	5.568%	$34.3729	$34.37	$34.35	$34.40
Purchase #5	$97.77	11.742%	$109.2502	$109.25	$109.25	$109.30
Purchase #6	$196.81	13.539%	$223.4561	$223.46	$223.45	$223.50
Purchase #7	$20.46	4.397%	$21.3596	$21.36	$21.35	$21.40
7 purchase totals =	$717.82		$789.2593	$789.25	$789.20	$789.50