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	$128.67	8.495%	$139.6005	$139.60	$139.60	$139.60
Purchase #2	$208.56	7.188%	$223.5513	$223.55	$223.55	$223.60
Purchase #3	$71.53	13.499%	$81.1858	$81.19	$81.20	$81.20
Purchase #4	$89.25	11.812%	$99.7922	$99.79	$99.80	$99.80
Purchase #5	$222.64	5.520%	$234.9297	$234.93	$234.95	$234.90
Purchase #6	$66.54	8.294%	$72.0588	$72.06	$72.05	$72.10
Purchase #7	$136.45	13.310%	$154.6115	$154.61	$154.60	$154.60
7 purchase totals =	$923.64		$1,005.7298	$1,005.73	$1,005.75	$1,005.80