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	$165.37	3.575%	$171.282	$171.28	$171.30	$171.30
Purchase #2	$235.67	8.331%	$255.3037	$255.30	$255.30	$255.30
Purchase #3	$60.75	5.164%	$63.8871	$63.89	$63.90	$63.90
Purchase #4	$17.98	11.300%	$20.0117	$20.01	$20.00	$20.00
Purchase #5	$79.62	11.778%	$88.9976	$89.00	$89.00	$89.00
Purchase #6	$78.82	6.651%	$84.0623	$84.06	$84.05	$84.10
Purchase #7	$25.72	5.145%	$27.0433	$27.04	$27.05	$27.00
7 purchase totals =	$663.93		$710.5877	$710.58	$710.60	$710.60