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	$31.32	6.232%	$33.2719	$33.27	$33.25	$33.30
Purchase #2	$25.33	4.248%	$26.406	$26.41	$26.40	$26.40
Purchase #3	$57.48	12.737%	$64.8012	$64.80	$64.80	$64.80
Purchase #4	$104.62	11.651%	$116.8093	$116.81	$116.80	$116.80
Purchase #5	$111.72	4.513%	$116.7619	$116.76	$116.75	$116.80
Purchase #6	$91.32	10.104%	$100.547	$100.55	$100.55	$100.50
Purchase #7	$55.43	12.243%	$62.2163	$62.22	$62.20	$62.20
7 purchase totals =	$477.22		$520.8136	$520.82	$520.75	$520.80