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	$80.42	12.174%	$90.2103	$90.21	$90.20	$90.20
Purchase #2	$47.79	4.213%	$49.8034	$49.80	$49.80	$49.80
Purchase #3	$69.65	12.532%	$78.3785	$78.38	$78.40	$78.40
Purchase #4	$150.45	12.824%	$169.7437	$169.74	$169.75	$169.70
Purchase #5	$12.79	7.869%	$13.7964	$13.80	$13.80	$13.80
Purchase #6	$50.44	4.865%	$52.8939	$52.89	$52.90	$52.90
Purchase #7	$248.50	11.510%	$277.1024	$277.10	$277.10	$277.10
7 purchase totals =	$660.04		$731.9286	$731.92	$731.95	$731.90