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	$17.26	12.204%	$19.3664	$19.37	$19.35	$19.40
Purchase #2	$76.59	13.404%	$86.8561	$86.86	$86.85	$86.90
Purchase #3	$40.54	12.624%	$45.6578	$45.66	$45.65	$45.70
Purchase #4	$79.41	7.292%	$85.2006	$85.20	$85.20	$85.20
Purchase #5	$37.84	6.826%	$40.423	$40.42	$40.40	$40.40
Purchase #6	$11.76	6.858%	$12.5665	$12.57	$12.55	$12.60
Purchase #7	$202.56	10.323%	$223.4703	$223.47	$223.45	$223.50
7 purchase totals =	$465.96		$513.5407	$513.55	$513.45	$513.70