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	$57.56	13.321%	$65.2276	$65.23	$65.25	$65.20
Purchase #2	$13.74	7.629%	$14.7882	$14.79	$14.80	$14.80
Purchase #3	$169.84	9.347%	$185.7149	$185.71	$185.70	$185.70
Purchase #4	$45.51	4.640%	$47.6217	$47.62	$47.60	$47.60
Purchase #5	$161.95	3.353%	$167.3802	$167.38	$167.40	$167.40
Purchase #6	$90.44	9.539%	$99.0671	$99.07	$99.05	$99.10
Purchase #7	$82.69	11.781%	$92.4317	$92.43	$92.45	$92.40
7 purchase totals =	$621.73		$672.2314	$672.23	$672.25	$672.20