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	$147.40	10.181%	$162.4068	$162.41	$162.40	$162.40
Purchase #2	$250.57	11.763%	$280.0445	$280.04	$280.05	$280.00
Purchase #3	$134.75	7.628%	$145.0287	$145.03	$145.05	$145.00
Purchase #4	$109.77	6.136%	$116.5055	$116.51	$116.50	$116.50
Purchase #5	$76.61	12.445%	$86.1441	$86.14	$86.15	$86.10
Purchase #6	$50.52	8.440%	$54.7839	$54.78	$54.80	$54.80
Purchase #7	$68.90	10.494%	$76.1304	$76.13	$76.15	$76.10
7 purchase totals =	$838.52		$921.0439	$921.04	$921.10	$920.90