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	$234.56	9.364%	$256.5242	$256.52	$256.50	$256.50
Purchase #2	$156.82	8.846%	$170.6923	$170.69	$170.70	$170.70
Purchase #3	$232.96	4.514%	$243.4758	$243.48	$243.50	$243.50
Purchase #4	$156.59	13.521%	$177.7625	$177.76	$177.75	$177.80
Purchase #5	$88.60	13.309%	$100.3918	$100.39	$100.40	$100.40
Purchase #6	$242.27	5.575%	$255.7766	$255.78	$255.80	$255.80
Purchase #7	$36.28	13.428%	$41.1517	$41.15	$41.15	$41.20
7 purchase totals =	$1,148.08		$1,245.7749	$1,245.77	$1,245.80	$1,245.90