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	$240.63	4.129%	$250.5656	$250.57	$250.55	$250.60
Purchase #2	$84.91	6.153%	$90.1345	$90.13	$90.15	$90.10
Purchase #3	$63.61	3.718%	$65.975	$65.98	$66.00	$66.00
Purchase #4	$73.45	3.546%	$76.0545	$76.05	$76.05	$76.10
Purchase #5	$159.86	12.283%	$179.4956	$179.50	$179.50	$179.50
Purchase #6	$172.67	5.713%	$182.5346	$182.53	$182.55	$182.50
Purchase #7	$157.75	7.171%	$169.0623	$169.06	$169.05	$169.10
7 purchase totals =	$952.88		$1,013.8221	$1,013.82	$1,013.85	$1,013.90