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	$10.39	8.411%	$11.2639	$11.26	$11.25	$11.30
Purchase #2	$143.45	5.530%	$151.3828	$151.38	$151.40	$151.40
Purchase #3	$126.93	12.328%	$142.5779	$142.58	$142.60	$142.60
Purchase #4	$178.58	12.380%	$200.6882	$200.69	$200.70	$200.70
Purchase #5	$112.89	12.419%	$126.9098	$126.91	$126.90	$126.90
Purchase #6	$163.40	10.347%	$180.307	$180.31	$180.30	$180.30
Purchase #7	$42.44	3.431%	$43.8961	$43.90	$43.90	$43.90
7 purchase totals =	$778.08		$857.0257	$857.03	$857.05	$857.10