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	$26.27	4.819%	$27.536	$27.54	$27.55	$27.50
Purchase #2	$177.77	10.508%	$196.4501	$196.45	$196.45	$196.50
Purchase #3	$172.67	7.278%	$185.2369	$185.24	$185.25	$185.20
Purchase #4	$68.76	6.352%	$73.1276	$73.13	$73.15	$73.10
Purchase #5	$129.73	3.745%	$134.5884	$134.59	$134.60	$134.60
Purchase #6	$208.64	7.523%	$224.336	$224.34	$224.35	$224.30
Purchase #7	$36.94	6.686%	$39.4098	$39.41	$39.40	$39.40
7 purchase totals =	$820.78		$880.6848	$880.70	$880.75	$880.60