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	$41.80	11.211%	$46.4862	$46.49	$46.50	$46.50
Purchase #2	$151.39	5.593%	$159.8572	$159.86	$159.85	$159.90
Purchase #3	$114.93	7.732%	$123.8164	$123.82	$123.80	$123.80
Purchase #4	$69.77	12.617%	$78.5729	$78.57	$78.55	$78.60
Purchase #5	$38.45	10.290%	$42.4065	$42.41	$42.40	$42.40
Purchase #6	$209.79	9.511%	$229.7431	$229.74	$229.75	$229.70
Purchase #7	$103.84	13.635%	$117.9986	$118.00	$118.00	$118.00
7 purchase totals =	$729.97		$798.8809	$798.89	$798.85	$798.90