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	$18.97	12.501%	$21.3414	$21.34	$21.35	$21.30
Purchase #2	$225.55	5.842%	$238.7266	$238.73	$238.75	$238.70
Purchase #3	$234.68	11.673%	$262.0742	$262.07	$262.05	$262.10
Purchase #4	$236.43	7.866%	$255.0276	$255.03	$255.05	$255.00
Purchase #5	$15.98	8.755%	$17.379	$17.38	$17.40	$17.40
Purchase #6	$165.89	3.571%	$171.8139	$171.81	$171.80	$171.80
Purchase #7	$33.81	11.553%	$37.7161	$37.72	$37.70	$37.70
7 purchase totals =	$931.31		$1,004.0788	$1,004.08	$1,004.10	$1,004.00