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	$34.41	8.238%	$37.2447	$37.24	$37.25	$37.20
Purchase #2	$191.34	4.719%	$200.3693	$200.37	$200.35	$200.40
Purchase #3	$230.73	3.369%	$238.5033	$238.50	$238.50	$238.50
Purchase #4	$165.44	8.230%	$179.0557	$179.06	$179.05	$179.10
Purchase #5	$85.38	5.672%	$90.2228	$90.22	$90.20	$90.20
Purchase #6	$19.50	11.651%	$21.7719	$21.77	$21.75	$21.80
Purchase #7	$40.45	9.788%	$44.4092	$44.41	$44.40	$44.40
7 purchase totals =	$767.25		$811.5769	$811.57	$811.50	$811.60