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	$97.74	13.553%	$110.9867	$110.99	$111.00	$111.00
Purchase #2	$248.90	8.543%	$270.1635	$270.16	$270.15	$270.20
Purchase #3	$11.99	12.656%	$13.5075	$13.51	$13.50	$13.50
Purchase #4	$244.85	13.484%	$277.8656	$277.87	$277.85	$277.90
Purchase #5	$249.56	8.187%	$269.9915	$269.99	$270.00	$270.00
Purchase #6	$78.46	13.593%	$89.1251	$89.13	$89.15	$89.10
Purchase #7	$90.81	5.659%	$95.9489	$95.95	$95.95	$95.90
7 purchase totals =	$1,022.31		$1,127.5888	$1,127.60	$1,127.60	$1,127.60