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	$30.28	9.870%	$33.2686	$33.27	$33.25	$33.30
Purchase #2	$156.53	10.874%	$173.5511	$173.55	$173.55	$173.60
Purchase #3	$164.83	9.266%	$180.1031	$180.10	$180.10	$180.10
Purchase #4	$143.83	6.229%	$152.7892	$152.79	$152.80	$152.80
Purchase #5	$226.27	11.599%	$252.5151	$252.52	$252.50	$252.50
Purchase #6	$28.88	10.199%	$31.8255	$31.83	$31.85	$31.80
Purchase #7	$49.93	3.772%	$51.8134	$51.81	$51.80	$51.80
7 purchase totals =	$800.55		$875.8660	$875.87	$875.85	$875.90