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	$72.72	10.386%	$80.2727	$80.27	$80.25	$80.30
Purchase #2	$127.27	5.185%	$133.8689	$133.87	$133.85	$133.90
Purchase #3	$220.97	11.717%	$246.8611	$246.86	$246.85	$246.90
Purchase #4	$115.75	3.231%	$119.4899	$119.49	$119.50	$119.50
Purchase #5	$148.82	11.730%	$166.2766	$166.28	$166.30	$166.30
Purchase #6	$145.98	13.334%	$165.445	$165.45	$165.45	$165.40
Purchase #7	$55.93	12.524%	$62.9347	$62.93	$62.95	$62.90
7 purchase totals =	$887.44		$975.1489	$975.15	$975.15	$975.20