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	$63.84	3.523%	$66.0891	$66.09	$66.10	$66.10
Purchase #2	$202.34	12.220%	$227.0659	$227.07	$227.05	$227.10
Purchase #3	$58.77	12.521%	$66.1286	$66.13	$66.15	$66.10
Purchase #4	$207.53	4.266%	$216.3832	$216.38	$216.40	$216.40
Purchase #5	$223.62	6.620%	$238.4236	$238.42	$238.40	$238.40
Purchase #6	$57.71	3.778%	$59.8903	$59.89	$59.90	$59.90
Purchase #7	$171.64	6.336%	$182.5151	$182.52	$182.50	$182.50
7 purchase totals =	$985.45		$1,056.4958	$1,056.50	$1,056.50	$1,056.50