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	$212.31	12.231%	$238.2776	$238.28	$238.30	$238.30
Purchase #2	$213.76	6.500%	$227.6544	$227.65	$227.65	$227.70
Purchase #3	$68.54	6.786%	$73.1911	$73.19	$73.20	$73.20
Purchase #4	$105.77	6.782%	$112.9433	$112.94	$112.95	$112.90
Purchase #5	$74.74	7.238%	$80.1497	$80.15	$80.15	$80.10
Purchase #6	$87.72	12.297%	$98.5069	$98.51	$98.50	$98.50
Purchase #7	$155.45	4.456%	$162.3769	$162.38	$162.40	$162.40
7 purchase totals =	$918.29		$993.0999	$993.10	$993.15	$993.10