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	$33.62	11.868%	$37.61	$37.61	$37.60	$37.60
Purchase #2	$123.42	10.510%	$136.3914	$136.39	$136.40	$136.40
Purchase #3	$236.40	9.255%	$258.2788	$258.28	$258.30	$258.30
Purchase #4	$131.99	8.368%	$143.0349	$143.03	$143.05	$143.00
Purchase #5	$120.85	11.199%	$134.384	$134.38	$134.40	$134.40
Purchase #6	$195.66	12.190%	$219.511	$219.51	$219.50	$219.50
Purchase #7	$68.88	6.799%	$73.5632	$73.56	$73.55	$73.60
7 purchase totals =	$910.82		$1,002.7733	$1,002.76	$1,002.80	$1,002.80