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	$32.98	9.488%	$36.1091	$36.11	$36.10	$36.10
Purchase #2	$100.60	10.757%	$111.4215	$111.42	$111.40	$111.40
Purchase #3	$212.52	10.484%	$234.8006	$234.80	$234.80	$234.80
Purchase #4	$35.74	7.190%	$38.3097	$38.31	$38.30	$38.30
Purchase #5	$205.76	12.345%	$231.1611	$231.16	$231.15	$231.20
Purchase #6	$184.40	7.631%	$198.4716	$198.47	$198.45	$198.50
Purchase #7	$110.66	11.574%	$123.4678	$123.47	$123.45	$123.50
7 purchase totals =	$882.66		$973.7414	$973.74	$973.65	$973.80