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	$32.38	12.166%	$36.3194	$36.32	$36.30	$36.30
Purchase #2	$29.33	10.236%	$32.3322	$32.33	$32.35	$32.30
Purchase #3	$156.43	8.578%	$169.8486	$169.85	$169.85	$169.80
Purchase #4	$37.64	11.179%	$41.8478	$41.85	$41.85	$41.80
Purchase #5	$63.42	10.447%	$70.0455	$70.05	$70.05	$70.00
Purchase #6	$6.42	11.358%	$7.1492	$7.15	$7.15	$7.10
Purchase #7	$231.44	11.426%	$257.8843	$257.88	$257.90	$257.90
7 purchase totals =	$557.06		$615.4270	$615.43	$615.45	$615.20