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	$58.35	13.398%	$66.1677	$66.17	$66.15	$66.20
Purchase #2	$213.89	12.370%	$240.3482	$240.35	$240.35	$240.30
Purchase #3	$146.65	12.436%	$164.8874	$164.89	$164.90	$164.90
Purchase #4	$66.70	9.241%	$72.8637	$72.86	$72.85	$72.90
Purchase #5	$162.53	12.845%	$183.407	$183.41	$183.40	$183.40
Purchase #6	$216.56	3.202%	$223.4943	$223.49	$223.50	$223.50
Purchase #7	$241.37	5.229%	$253.9912	$253.99	$254.00	$254.00
7 purchase totals =	$1,106.05		$1,205.1595	$1,205.16	$1,205.15	$1,205.20