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	$18.70	11.305%	$20.814	$20.81	$20.80	$20.80
Purchase #2	$88.56	8.238%	$95.8556	$95.86	$95.85	$95.90
Purchase #3	$93.83	10.346%	$103.5377	$103.54	$103.55	$103.50
Purchase #4	$96.45	13.377%	$109.3521	$109.35	$109.35	$109.40
Purchase #5	$169.53	5.822%	$179.4	$179.40	$179.40	$179.40
Purchase #6	$121.77	10.789%	$134.9078	$134.91	$134.90	$134.90
Purchase #7	$129.45	13.560%	$147.0034	$147.00	$147.00	$147.00
7 purchase totals =	$718.29		$790.8706	$790.87	$790.85	$790.90