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	$121.57	4.745%	$127.3385	$127.34	$127.35	$127.30
Purchase #2	$45.73	11.455%	$50.9684	$50.97	$50.95	$51.00
Purchase #3	$58.45	3.573%	$60.5384	$60.54	$60.55	$60.50
Purchase #4	$166.53	3.584%	$172.4984	$172.50	$172.50	$172.50
Purchase #5	$174.37	6.416%	$185.5576	$185.56	$185.55	$185.60
Purchase #6	$92.98	3.622%	$96.3477	$96.35	$96.35	$96.30
Purchase #7	$249.45	10.321%	$275.1957	$275.20	$275.20	$275.20
7 purchase totals =	$909.08		$968.4447	$968.46	$968.45	$968.40