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	$28.30	3.423%	$29.2687	$29.27	$29.25	$29.30
Purchase #2	$119.62	6.779%	$127.729	$127.73	$127.75	$127.70
Purchase #3	$209.80	6.203%	$222.8139	$222.81	$222.80	$222.80
Purchase #4	$114.36	8.800%	$124.4237	$124.42	$124.40	$124.40
Purchase #5	$17.81	10.737%	$19.7223	$19.72	$19.70	$19.70
Purchase #6	$166.88	11.408%	$185.9177	$185.92	$185.90	$185.90
Purchase #7	$20.54	3.592%	$21.2778	$21.28	$21.30	$21.30
7 purchase totals =	$677.31		$731.1531	$731.15	$731.10	$731.10