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	$40.89	4.707%	$42.8147	$42.81	$42.80	$42.80
Purchase #2	$232.98	8.805%	$253.4939	$253.49	$253.50	$253.50
Purchase #3	$82.27	12.315%	$92.4016	$92.40	$92.40	$92.40
Purchase #4	$54.69	13.396%	$62.0163	$62.02	$62.00	$62.00
Purchase #5	$19.56	12.189%	$21.9442	$21.94	$21.95	$21.90
Purchase #6	$140.85	11.175%	$156.59	$156.59	$156.60	$156.60
Purchase #7	$169.41	11.213%	$188.4059	$188.41	$188.40	$188.40
7 purchase totals =	$740.65		$817.6666	$817.66	$817.65	$817.60