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	$27.58	13.487%	$31.2997	$31.30	$31.30	$31.30
Purchase #2	$34.31	11.706%	$38.3263	$38.33	$38.35	$38.30
Purchase #3	$250.57	5.474%	$264.2862	$264.29	$264.30	$264.30
Purchase #4	$159.86	13.761%	$181.8583	$181.86	$181.85	$181.90
Purchase #5	$57.25	10.107%	$63.0363	$63.04	$63.05	$63.00
Purchase #6	$219.65	11.493%	$244.8944	$244.89	$244.90	$244.90
Purchase #7	$114.27	12.509%	$128.564	$128.56	$128.55	$128.60
7 purchase totals =	$863.49		$952.2652	$952.27	$952.30	$952.30