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	$74.79	5.327%	$78.7741	$78.77	$78.75	$78.80
Purchase #2	$17.67	6.786%	$18.8691	$18.87	$18.85	$18.90
Purchase #3	$86.79	10.482%	$95.8873	$95.89	$95.90	$95.90
Purchase #4	$10.99	7.269%	$11.7889	$11.79	$11.80	$11.80
Purchase #5	$109.67	12.429%	$123.3009	$123.30	$123.30	$123.30
Purchase #6	$6.84	12.587%	$7.701	$7.70	$7.70	$7.70
Purchase #7	$211.72	5.232%	$222.7972	$222.80	$222.80	$222.80
7 purchase totals =	$518.47		$559.1185	$559.12	$559.10	$559.20