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	$90.81	13.744%	$103.2909	$103.29	$103.30	$103.30
Purchase #2	$216.87	10.635%	$239.9341	$239.93	$239.95	$239.90
Purchase #3	$116.59	9.281%	$127.4107	$127.41	$127.40	$127.40
Purchase #4	$48.47	11.154%	$53.8763	$53.88	$53.90	$53.90
Purchase #5	$76.66	8.553%	$83.2167	$83.22	$83.20	$83.20
Purchase #6	$182.61	4.600%	$191.0101	$191.01	$191.00	$191.00
Purchase #7	$139.78	5.220%	$147.0765	$147.08	$147.10	$147.10
7 purchase totals =	$871.79		$945.8153	$945.82	$945.85	$945.80