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	$218.42	10.793%	$241.9941	$241.99	$242.00	$242.00
Purchase #2	$144.62	6.866%	$154.5496	$154.55	$154.55	$154.50
Purchase #3	$79.29	8.291%	$85.8639	$85.86	$85.85	$85.90
Purchase #4	$100.91	3.549%	$104.4913	$104.49	$104.50	$104.50
Purchase #5	$88.99	11.674%	$99.3787	$99.38	$99.40	$99.40
Purchase #6	$146.89	13.573%	$166.8274	$166.83	$166.85	$166.80
Purchase #7	$108.34	13.586%	$123.0591	$123.06	$123.05	$123.10
7 purchase totals =	$887.46		$976.1641	$976.16	$976.20	$976.20