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	$61.61	5.322%	$64.8889	$64.89	$64.90	$64.90
Purchase #2	$36.82	10.428%	$40.6596	$40.66	$40.65	$40.70
Purchase #3	$90.48	10.525%	$100.003	$100.00	$100.00	$100.00
Purchase #4	$31.90	11.235%	$35.484	$35.48	$35.50	$35.50
Purchase #5	$183.91	10.775%	$203.7263	$203.73	$203.75	$203.70
Purchase #6	$98.43	9.866%	$108.1411	$108.14	$108.15	$108.10
Purchase #7	$142.87	5.259%	$150.3835	$150.38	$150.40	$150.40
7 purchase totals =	$646.02		$703.2864	$703.28	$703.35	$703.30