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	$25.25	8.453%	$27.3844	$27.38	$27.40	$27.40
Purchase #2	$163.84	13.472%	$185.9125	$185.91	$185.90	$185.90
Purchase #3	$125.75	13.393%	$142.5917	$142.59	$142.60	$142.60
Purchase #4	$205.71	3.680%	$213.2801	$213.28	$213.30	$213.30
Purchase #5	$134.82	7.116%	$144.4138	$144.41	$144.40	$144.40
Purchase #6	$241.74	11.628%	$269.8495	$269.85	$269.85	$269.80
Purchase #7	$59.27	5.234%	$62.3722	$62.37	$62.35	$62.40
7 purchase totals =	$956.38		$1,045.8042	$1,045.79	$1,045.80	$1,045.80