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	$114.83	12.102%	$128.7267	$128.73	$128.75	$128.70
Purchase #2	$46.72	13.466%	$53.0113	$53.01	$53.00	$53.00
Purchase #3	$215.53	10.620%	$238.4193	$238.42	$238.40	$238.40
Purchase #4	$85.55	10.206%	$94.2812	$94.28	$94.30	$94.30
Purchase #5	$184.74	13.817%	$210.2655	$210.27	$210.25	$210.30
Purchase #6	$43.82	11.555%	$48.8834	$48.88	$48.90	$48.90
Purchase #7	$42.97	12.835%	$48.4852	$48.49	$48.50	$48.50
7 purchase totals =	$734.16		$822.0726	$822.08	$822.10	$822.10