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	$122.87	11.763%	$137.3232	$137.32	$137.30	$137.30
Purchase #2	$246.69	12.653%	$277.9037	$277.90	$277.90	$277.90
Purchase #3	$79.96	11.172%	$88.8931	$88.89	$88.90	$88.90
Purchase #4	$81.49	9.835%	$89.5045	$89.50	$89.50	$89.50
Purchase #5	$222.63	7.609%	$239.5699	$239.57	$239.55	$239.60
Purchase #6	$182.42	10.124%	$200.8882	$200.89	$200.90	$200.90
Purchase #7	$125.33	10.151%	$138.0522	$138.05	$138.05	$138.10
7 purchase totals =	$1,061.39		$1,172.1348	$1,172.12	$1,172.10	$1,172.20