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	$11.66	7.326%	$12.5142	$12.51	$12.50	$12.50
Purchase #2	$6.87	8.799%	$7.4745	$7.47	$7.45	$7.50
Purchase #3	$174.96	5.700%	$184.9327	$184.93	$184.95	$184.90
Purchase #4	$46.96	9.231%	$51.2949	$51.29	$51.30	$51.30
Purchase #5	$38.56	5.244%	$40.5821	$40.58	$40.60	$40.60
Purchase #6	$190.93	12.729%	$215.2335	$215.23	$215.25	$215.20
Purchase #7	$115.52	7.258%	$123.9044	$123.90	$123.90	$123.90
7 purchase totals =	$585.46		$635.9363	$635.91	$635.95	$635.90