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	$248.57	12.349%	$279.2659	$279.27	$279.25	$279.30
Purchase #2	$28.60	12.342%	$32.1298	$32.13	$32.15	$32.10
Purchase #3	$65.68	7.387%	$70.5318	$70.53	$70.55	$70.50
Purchase #4	$68.73	3.133%	$70.8833	$70.88	$70.90	$70.90
Purchase #5	$57.78	7.506%	$62.117	$62.12	$62.10	$62.10
Purchase #6	$249.83	5.102%	$262.5763	$262.58	$262.60	$262.60
Purchase #7	$209.72	11.511%	$233.8609	$233.86	$233.85	$233.90
7 purchase totals =	$928.91		$1,011.3650	$1,011.37	$1,011.40	$1,011.40