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	$58.38	13.600%	$66.3197	$66.32	$66.30	$66.30
Purchase #2	$57.52	12.313%	$64.6024	$64.60	$64.60	$64.60
Purchase #3	$54.25	4.761%	$56.8328	$56.83	$56.85	$56.80
Purchase #4	$237.41	12.263%	$266.5236	$266.52	$266.50	$266.50
Purchase #5	$167.34	4.442%	$174.7732	$174.77	$174.75	$174.80
Purchase #6	$70.34	7.246%	$75.4368	$75.44	$75.45	$75.40
Purchase #7	$140.48	8.531%	$152.4643	$152.46	$152.45	$152.50
7 purchase totals =	$785.72		$856.9528	$856.94	$856.90	$856.90