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	$51.38	10.173%	$56.6069	$56.61	$56.60	$56.60
Purchase #2	$92.95	7.172%	$99.6164	$99.62	$99.60	$99.60
Purchase #3	$36.28	7.155%	$38.8758	$38.88	$38.90	$38.90
Purchase #4	$137.93	10.452%	$152.3464	$152.35	$152.35	$152.30
Purchase #5	$19.73	6.796%	$21.0709	$21.07	$21.05	$21.10
Purchase #6	$148.80	5.674%	$157.2429	$157.24	$157.25	$157.20
Purchase #7	$82.47	7.674%	$88.7987	$88.80	$88.80	$88.80
7 purchase totals =	$569.54		$614.5580	$614.57	$614.55	$614.50