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	$109.82	5.365%	$115.7118	$115.71	$115.70	$115.70
Purchase #2	$236.76	7.351%	$254.1642	$254.16	$254.15	$254.20
Purchase #3	$138.44	13.469%	$157.0865	$157.09	$157.10	$157.10
Purchase #4	$177.54	10.693%	$196.5244	$196.52	$196.50	$196.50
Purchase #5	$104.56	10.406%	$115.4405	$115.44	$115.45	$115.40
Purchase #6	$56.77	4.380%	$59.2565	$59.26	$59.25	$59.30
Purchase #7	$90.85	11.432%	$101.236	$101.24	$101.25	$101.20
7 purchase totals =	$914.74		$999.4199	$999.42	$999.40	$999.40