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	$237.25	3.574%	$245.7293	$245.73	$245.75	$245.70
Purchase #2	$95.26	12.554%	$107.2189	$107.22	$107.20	$107.20
Purchase #3	$116.35	13.175%	$131.6791	$131.68	$131.70	$131.70
Purchase #4	$90.28	10.624%	$99.8713	$99.87	$99.85	$99.90
Purchase #5	$30.72	7.420%	$32.9994	$33.00	$33.00	$33.00
Purchase #6	$130.31	11.603%	$145.4299	$145.43	$145.45	$145.40
Purchase #7	$126.59	12.538%	$142.4619	$142.46	$142.45	$142.50
7 purchase totals =	$826.76		$905.3898	$905.39	$905.40	$905.40