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	$121.76	12.321%	$136.762	$136.76	$136.75	$136.80
Purchase #2	$50.40	7.147%	$54.0021	$54.00	$54.00	$54.00
Purchase #3	$78.89	4.427%	$82.3825	$82.38	$82.40	$82.40
Purchase #4	$110.98	4.606%	$116.0917	$116.09	$116.10	$116.10
Purchase #5	$93.79	12.737%	$105.736	$105.74	$105.75	$105.70
Purchase #6	$19.72	3.185%	$20.3481	$20.35	$20.35	$20.30
Purchase #7	$244.86	5.688%	$258.7876	$258.79	$258.80	$258.80
7 purchase totals =	$720.40		$774.1100	$774.11	$774.15	$774.10