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	$155.56	8.456%	$168.7142	$168.71	$168.70	$168.70
Purchase #2	$105.54	6.449%	$112.3463	$112.35	$112.35	$112.30
Purchase #3	$70.28	11.761%	$78.5456	$78.55	$78.55	$78.50
Purchase #4	$10.75	11.788%	$12.0172	$12.02	$12.00	$12.00
Purchase #5	$56.42	13.305%	$63.9267	$63.93	$63.95	$63.90
Purchase #6	$81.79	9.821%	$89.8226	$89.82	$89.80	$89.80
Purchase #7	$126.77	6.813%	$135.4068	$135.41	$135.40	$135.40
7 purchase totals =	$607.11		$660.7794	$660.79	$660.75	$660.60