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	$132.74	3.157%	$136.9306	$136.93	$136.95	$136.90
Purchase #2	$44.29	11.389%	$49.3342	$49.33	$49.35	$49.30
Purchase #3	$165.72	7.632%	$178.3678	$178.37	$178.35	$178.40
Purchase #4	$216.83	5.561%	$228.8879	$228.89	$228.90	$228.90
Purchase #5	$167.32	9.802%	$183.7207	$183.72	$183.70	$183.70
Purchase #6	$100.88	11.514%	$112.4953	$112.50	$112.50	$112.50
Purchase #7	$83.94	9.518%	$91.9294	$91.93	$91.95	$91.90
7 purchase totals =	$911.72		$981.6659	$981.67	$981.70	$981.60