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	$31.43	3.657%	$32.5794	$32.58	$32.60	$32.60
Purchase #2	$82.25	13.461%	$93.3217	$93.32	$93.30	$93.30
Purchase #3	$154.92	4.589%	$162.0293	$162.03	$162.05	$162.00
Purchase #4	$29.71	3.586%	$30.7754	$30.78	$30.80	$30.80
Purchase #5	$37.93	11.295%	$42.2142	$42.21	$42.20	$42.20
Purchase #6	$139.77	5.812%	$147.8934	$147.89	$147.90	$147.90
Purchase #7	$66.78	9.123%	$72.8723	$72.87	$72.85	$72.90
7 purchase totals =	$542.79		$581.6857	$581.68	$581.70	$581.70