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	$21.71	7.473%	$23.3324	$23.33	$23.35	$23.30
Purchase #2	$24.71	3.583%	$25.5954	$25.60	$25.60	$25.60
Purchase #3	$31.57	4.195%	$32.8944	$32.89	$32.90	$32.90
Purchase #4	$213.88	6.481%	$227.7416	$227.74	$227.75	$227.70
Purchase #5	$63.62	11.615%	$71.0095	$71.01	$71.00	$71.00
Purchase #6	$233.67	13.660%	$265.5893	$265.59	$265.60	$265.60
Purchase #7	$156.59	10.424%	$172.9129	$172.91	$172.90	$172.90
7 purchase totals =	$745.75		$819.0755	$819.07	$819.10	$819.00