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	$97.71	8.345%	$105.8639	$105.86	$105.85	$105.90
Purchase #2	$104.97	4.606%	$109.8049	$109.80	$109.80	$109.80
Purchase #3	$236.81	10.559%	$261.8148	$261.81	$261.80	$261.80
Purchase #4	$65.82	7.356%	$70.6617	$70.66	$70.65	$70.70
Purchase #5	$6.86	5.734%	$7.2534	$7.25	$7.25	$7.30
Purchase #6	$249.56	10.520%	$275.8137	$275.81	$275.80	$275.80
Purchase #7	$38.92	6.765%	$41.5529	$41.55	$41.55	$41.60
7 purchase totals =	$800.65		$872.7653	$872.74	$872.70	$872.90