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	$10.76	4.803%	$11.2768	$11.28	$11.30	$11.30
Purchase #2	$37.43	7.460%	$40.2223	$40.22	$40.20	$40.20
Purchase #3	$103.44	5.467%	$109.0951	$109.10	$109.10	$109.10
Purchase #4	$227.70	7.858%	$245.5927	$245.59	$245.60	$245.60
Purchase #5	$236.72	13.650%	$269.0323	$269.03	$269.05	$269.00
Purchase #6	$70.86	13.563%	$80.4707	$80.47	$80.45	$80.50
Purchase #7	$17.49	4.247%	$18.2328	$18.23	$18.25	$18.20
7 purchase totals =	$704.40		$773.9227	$773.92	$773.95	$773.90