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	$173.92	7.822%	$187.524	$187.52	$187.50	$187.50
Purchase #2	$64.71	4.167%	$67.4065	$67.41	$67.40	$67.40
Purchase #3	$154.72	3.362%	$159.9217	$159.92	$159.90	$159.90
Purchase #4	$24.79	9.736%	$27.2036	$27.20	$27.20	$27.20
Purchase #5	$113.30	9.872%	$124.485	$124.49	$124.50	$124.50
Purchase #6	$53.79	6.622%	$57.352	$57.35	$57.35	$57.40
Purchase #7	$40.35	12.352%	$45.334	$45.33	$45.35	$45.30
7 purchase totals =	$625.58		$669.2268	$669.22	$669.20	$669.20