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	$223.87	6.505%	$238.4327	$238.43	$238.45	$238.40
Purchase #2	$228.25	12.127%	$255.9299	$255.93	$255.95	$255.90
Purchase #3	$118.71	11.132%	$131.9248	$131.92	$131.90	$131.90
Purchase #4	$161.68	7.710%	$174.1455	$174.15	$174.15	$174.10
Purchase #5	$169.36	11.649%	$189.0887	$189.09	$189.10	$189.10
Purchase #6	$142.32	10.225%	$156.8722	$156.87	$156.85	$156.90
Purchase #7	$17.86	8.811%	$19.4336	$19.43	$19.45	$19.40
7 purchase totals =	$1,062.05		$1,165.8274	$1,165.82	$1,165.85	$1,165.70