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	$25.42	13.474%	$28.8451	$28.85	$28.85	$28.80
Purchase #2	$38.59	5.453%	$40.6943	$40.69	$40.70	$40.70
Purchase #3	$195.83	8.712%	$212.8907	$212.89	$212.90	$212.90
Purchase #4	$153.98	3.133%	$158.8042	$158.80	$158.80	$158.80
Purchase #5	$164.86	12.393%	$185.2911	$185.29	$185.30	$185.30
Purchase #6	$24.50	12.332%	$27.5213	$27.52	$27.50	$27.50
Purchase #7	$173.33	11.209%	$192.7586	$192.76	$192.75	$192.80
7 purchase totals =	$776.51		$846.8053	$846.80	$846.80	$846.80