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	$109.42	3.178%	$112.8974	$112.90	$112.90	$112.90
Purchase #2	$87.73	13.181%	$99.2937	$99.29	$99.30	$99.30
Purchase #3	$123.90	7.174%	$132.7886	$132.79	$132.80	$132.80
Purchase #4	$205.45	7.727%	$221.3251	$221.33	$221.35	$221.30
Purchase #5	$127.83	3.653%	$132.4996	$132.50	$132.50	$132.50
Purchase #6	$20.61	8.310%	$22.3227	$22.32	$22.30	$22.30
Purchase #7	$103.32	10.822%	$114.5013	$114.50	$114.50	$114.50
7 purchase totals =	$778.26		$835.6284	$835.63	$835.65	$835.60