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	$38.42	4.820%	$40.2718	$40.27	$40.25	$40.30
Purchase #2	$88.63	12.103%	$99.3569	$99.36	$99.35	$99.40
Purchase #3	$18.91	10.719%	$20.937	$20.94	$20.95	$20.90
Purchase #4	$190.26	10.863%	$210.9279	$210.93	$210.95	$210.90
Purchase #5	$136.83	13.553%	$155.3746	$155.37	$155.35	$155.40
Purchase #6	$53.96	13.255%	$61.1124	$61.11	$61.10	$61.10
Purchase #7	$73.56	10.199%	$81.0624	$81.06	$81.05	$81.10
7 purchase totals =	$600.57		$669.0430	$669.04	$669.00	$669.10