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	$18.89	13.545%	$21.4487	$21.45	$21.45	$21.40
Purchase #2	$171.89	9.848%	$188.8177	$188.82	$188.80	$188.80
Purchase #3	$36.38	3.735%	$37.7388	$37.74	$37.75	$37.70
Purchase #4	$137.61	9.864%	$151.1839	$151.18	$151.20	$151.20
Purchase #5	$145.89	12.743%	$164.4808	$164.48	$164.50	$164.50
Purchase #6	$37.79	11.280%	$42.0527	$42.05	$42.05	$42.10
Purchase #7	$171.69	5.313%	$180.8119	$180.81	$180.80	$180.80
7 purchase totals =	$720.14		$786.5345	$786.53	$786.55	$786.50