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	$17.85	3.217%	$18.4242	$18.42	$18.40	$18.40
Purchase #2	$245.52	12.346%	$275.8319	$275.83	$275.85	$275.80
Purchase #3	$142.60	9.844%	$156.6375	$156.64	$156.65	$156.60
Purchase #4	$73.31	6.373%	$77.982	$77.98	$78.00	$78.00
Purchase #5	$36.86	6.519%	$39.2629	$39.26	$39.25	$39.30
Purchase #6	$137.51	9.323%	$150.3301	$150.33	$150.35	$150.30
Purchase #7	$50.83	8.452%	$55.1262	$55.13	$55.15	$55.10
7 purchase totals =	$704.48		$773.5948	$773.59	$773.65	$773.50