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	$222.40	6.740%	$237.3898	$237.39	$237.40	$237.40
Purchase #2	$87.74	8.380%	$95.0926	$95.09	$95.10	$95.10
Purchase #3	$157.59	12.294%	$176.9641	$176.96	$176.95	$177.00
Purchase #4	$81.47	5.743%	$86.1488	$86.15	$86.15	$86.10
Purchase #5	$250.90	11.612%	$280.0345	$280.03	$280.05	$280.00
Purchase #6	$172.35	5.217%	$181.3415	$181.34	$181.35	$181.30
Purchase #7	$36.40	11.633%	$40.6344	$40.63	$40.65	$40.60
7 purchase totals =	$1,008.85		$1,097.6057	$1,097.59	$1,097.65	$1,097.50