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	$35.86	7.118%	$38.4125	$38.41	$38.40	$38.40
Purchase #2	$52.76	3.502%	$54.6077	$54.61	$54.60	$54.60
Purchase #3	$106.89	13.431%	$121.2464	$121.25	$121.25	$121.20
Purchase #4	$152.85	8.490%	$165.827	$165.83	$165.85	$165.80
Purchase #5	$164.52	3.332%	$170.0018	$170.00	$170.00	$170.00
Purchase #6	$151.90	8.653%	$165.0439	$165.04	$165.05	$165.00
Purchase #7	$11.83	10.218%	$13.0388	$13.04	$13.05	$13.00
7 purchase totals =	$676.61		$728.1781	$728.18	$728.20	$728.00