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	$250.26	11.245%	$278.4017	$278.40	$278.40	$278.40
Purchase #2	$95.55	3.608%	$98.9974	$99.00	$99.00	$99.00
Purchase #3	$173.40	10.128%	$190.962	$190.96	$190.95	$191.00
Purchase #4	$124.73	7.786%	$134.4415	$134.44	$134.45	$134.40
Purchase #5	$168.54	9.686%	$184.8648	$184.86	$184.85	$184.90
Purchase #6	$90.91	5.356%	$95.7791	$95.78	$95.80	$95.80
Purchase #7	$12.52	10.137%	$13.7892	$13.79	$13.80	$13.80
7 purchase totals =	$915.91		$997.2357	$997.23	$997.25	$997.30