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	$17.53	6.603%	$18.6875	$18.69	$18.70	$18.70
Purchase #2	$116.44	10.667%	$128.8607	$128.86	$128.85	$128.90
Purchase #3	$169.95	3.752%	$176.3265	$176.33	$176.35	$176.30
Purchase #4	$71.25	12.492%	$80.1506	$80.15	$80.15	$80.20
Purchase #5	$63.54	12.159%	$71.2658	$71.27	$71.25	$71.30
Purchase #6	$164.45	10.373%	$181.5084	$181.51	$181.50	$181.50
Purchase #7	$131.25	10.721%	$145.3213	$145.32	$145.30	$145.30
7 purchase totals =	$734.41		$802.1208	$802.13	$802.10	$802.20