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	$33.37	12.416%	$37.5132	$37.51	$37.50	$37.50
Purchase #2	$32.98	6.291%	$35.0548	$35.05	$35.05	$35.10
Purchase #3	$19.76	8.435%	$21.4268	$21.43	$21.45	$21.40
Purchase #4	$196.58	6.320%	$209.0039	$209.00	$209.00	$209.00
Purchase #5	$223.94	13.661%	$254.5324	$254.53	$254.55	$254.50
Purchase #6	$77.61	7.134%	$83.1467	$83.15	$83.15	$83.10
Purchase #7	$140.60	4.491%	$146.9143	$146.91	$146.90	$146.90
7 purchase totals =	$724.84		$787.5921	$787.58	$787.60	$787.50