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	$55.27	12.815%	$62.3529	$62.35	$62.35	$62.40
Purchase #2	$196.46	3.134%	$202.6171	$202.62	$202.60	$202.60
Purchase #3	$150.92	11.130%	$167.7174	$167.72	$167.70	$167.70
Purchase #4	$43.68	10.680%	$48.345	$48.35	$48.35	$48.30
Purchase #5	$30.44	9.796%	$33.4219	$33.42	$33.40	$33.40
Purchase #6	$85.44	6.185%	$90.7245	$90.72	$90.70	$90.70
Purchase #7	$34.57	9.615%	$37.8939	$37.89	$37.90	$37.90
7 purchase totals =	$596.78		$643.0727	$643.07	$643.00	$643.00