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	$34.94	6.134%	$37.0832	$37.08	$37.10	$37.10
Purchase #2	$137.97	4.740%	$144.5098	$144.51	$144.50	$144.50
Purchase #3	$154.73	13.734%	$175.9806	$175.98	$176.00	$176.00
Purchase #4	$92.89	11.191%	$103.2853	$103.29	$103.30	$103.30
Purchase #5	$236.94	12.740%	$267.1262	$267.13	$267.15	$267.10
Purchase #6	$144.43	5.275%	$152.0487	$152.05	$152.05	$152.00
Purchase #7	$202.36	10.436%	$223.4783	$223.48	$223.50	$223.50
7 purchase totals =	$1,004.26		$1,103.5121	$1,103.52	$1,103.60	$1,103.50