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	$19.86	7.448%	$21.3392	$21.34	$21.35	$21.30
Purchase #2	$221.53	5.874%	$234.5427	$234.54	$234.55	$234.50
Purchase #3	$176.71	5.865%	$187.074	$187.07	$187.05	$187.10
Purchase #4	$11.33	9.313%	$12.3852	$12.39	$12.40	$12.40
Purchase #5	$100.47	8.823%	$109.3345	$109.33	$109.35	$109.30
Purchase #6	$43.83	3.675%	$45.4408	$45.44	$45.45	$45.40
Purchase #7	$154.52	6.154%	$164.0292	$164.03	$164.05	$164.00
7 purchase totals =	$728.25		$774.1456	$774.14	$774.20	$774.00