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	$170.84	8.158%	$184.7771	$184.78	$184.80	$184.80
Purchase #2	$103.97	10.199%	$114.5739	$114.57	$114.55	$114.60
Purchase #3	$174.72	3.862%	$181.4677	$181.47	$181.45	$181.50
Purchase #4	$210.70	5.810%	$222.9417	$222.94	$222.95	$222.90
Purchase #5	$36.62	10.392%	$40.4256	$40.43	$40.45	$40.40
Purchase #6	$131.78	9.506%	$144.307	$144.31	$144.30	$144.30
Purchase #7	$79.41	13.356%	$90.016	$90.02	$90.00	$90.00
7 purchase totals =	$908.04		$978.5090	$978.52	$978.50	$978.50