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	$77.84	3.278%	$80.3916	$80.39	$80.40	$80.40
Purchase #2	$92.48	6.197%	$98.211	$98.21	$98.20	$98.20
Purchase #3	$65.60	7.393%	$70.4498	$70.45	$70.45	$70.40
Purchase #4	$206.25	12.390%	$231.8044	$231.80	$231.80	$231.80
Purchase #5	$122.56	13.759%	$139.423	$139.42	$139.40	$139.40
Purchase #6	$83.87	7.123%	$89.8441	$89.84	$89.85	$89.80
Purchase #7	$187.67	6.678%	$200.2026	$200.20	$200.20	$200.20
7 purchase totals =	$836.27		$910.3265	$910.31	$910.30	$910.20