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	$79.50	3.692%	$82.4351	$82.44	$82.45	$82.40
Purchase #2	$188.52	11.401%	$210.0132	$210.01	$210.00	$210.00
Purchase #3	$90.39	7.824%	$97.4621	$97.46	$97.45	$97.50
Purchase #4	$133.69	11.358%	$148.8745	$148.87	$148.85	$148.90
Purchase #5	$67.63	7.677%	$72.822	$72.82	$72.80	$72.80
Purchase #6	$76.32	5.803%	$80.7488	$80.75	$80.75	$80.70
Purchase #7	$135.82	13.812%	$154.5795	$154.58	$154.60	$154.60
7 purchase totals =	$771.87		$846.9352	$846.93	$846.90	$846.90