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	$72.90	12.659%	$82.1284	$82.13	$82.15	$82.10
Purchase #2	$143.32	6.553%	$152.7118	$152.71	$152.70	$152.70
Purchase #3	$205.85	12.291%	$231.151	$231.15	$231.15	$231.20
Purchase #4	$108.60	11.627%	$121.2269	$121.23	$121.25	$121.20
Purchase #5	$43.56	9.167%	$47.5531	$47.55	$47.55	$47.60
Purchase #6	$54.73	6.609%	$58.3471	$58.35	$58.35	$58.30
Purchase #7	$32.92	9.162%	$35.9361	$35.94	$35.95	$35.90
7 purchase totals =	$661.88		$729.0544	$729.06	$729.10	$729.00