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	$231.38	5.794%	$244.7862	$244.79	$244.80	$244.80
Purchase #2	$219.55	6.385%	$233.5683	$233.57	$233.55	$233.60
Purchase #3	$48.85	11.518%	$54.4765	$54.48	$54.50	$54.50
Purchase #4	$149.25	11.368%	$166.2167	$166.22	$166.20	$166.20
Purchase #5	$198.41	8.473%	$215.2213	$215.22	$215.20	$215.20
Purchase #6	$77.82	7.702%	$83.8137	$83.81	$83.80	$83.80
Purchase #7	$82.31	12.579%	$92.6638	$92.66	$92.65	$92.70
7 purchase totals =	$1,007.57		$1,090.7465	$1,090.75	$1,090.70	$1,090.80