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	$86.25	3.539%	$89.3024	$89.30	$89.30	$89.30
Purchase #2	$99.76	3.483%	$103.2346	$103.23	$103.25	$103.20
Purchase #3	$194.42	3.112%	$200.4704	$200.47	$200.45	$200.50
Purchase #4	$55.48	7.742%	$59.7753	$59.78	$59.80	$59.80
Purchase #5	$228.64	11.839%	$255.7087	$255.71	$255.70	$255.70
Purchase #6	$140.78	7.231%	$150.9598	$150.96	$150.95	$151.00
Purchase #7	$38.96	13.384%	$44.1744	$44.17	$44.15	$44.20
7 purchase totals =	$844.29		$903.6256	$903.62	$903.60	$903.70