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	$40.80	4.557%	$42.6593	$42.66	$42.65	$42.70
Purchase #2	$134.54	8.831%	$146.4212	$146.42	$146.40	$146.40
Purchase #3	$90.82	6.528%	$96.7487	$96.75	$96.75	$96.70
Purchase #4	$30.63	7.240%	$32.8476	$32.85	$32.85	$32.80
Purchase #5	$139.26	6.543%	$148.3718	$148.37	$148.35	$148.40
Purchase #6	$215.57	11.295%	$239.9186	$239.92	$239.90	$239.90
Purchase #7	$53.43	7.759%	$57.5756	$57.58	$57.60	$57.60
7 purchase totals =	$705.05		$764.5428	$764.55	$764.50	$764.50