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	$169.72	5.471%	$179.0054	$179.01	$179.00	$179.00
Purchase #2	$237.98	3.107%	$245.374	$245.37	$245.35	$245.40
Purchase #3	$80.41	12.677%	$90.6036	$90.60	$90.60	$90.60
Purchase #4	$218.43	9.819%	$239.8776	$239.88	$239.90	$239.90
Purchase #5	$167.45	9.375%	$183.1484	$183.15	$183.15	$183.10
Purchase #6	$67.45	8.105%	$72.9168	$72.92	$72.90	$72.90
Purchase #7	$71.41	9.682%	$78.3239	$78.32	$78.30	$78.30
7 purchase totals =	$1,012.85		$1,089.2497	$1,089.25	$1,089.20	$1,089.20