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	$228.60	11.726%	$255.4056	$255.41	$255.40	$255.40
Purchase #2	$107.74	6.210%	$114.4307	$114.43	$114.45	$114.40
Purchase #3	$26.98	12.852%	$30.4475	$30.45	$30.45	$30.40
Purchase #4	$123.99	5.165%	$130.3941	$130.39	$130.40	$130.40
Purchase #5	$212.95	11.871%	$238.2293	$238.23	$238.25	$238.20
Purchase #6	$59.72	6.514%	$63.6102	$63.61	$63.60	$63.60
Purchase #7	$89.61	10.618%	$99.1248	$99.12	$99.10	$99.10
7 purchase totals =	$849.59		$931.6422	$931.64	$931.65	$931.50