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	$165.66	6.552%	$176.514	$176.51	$176.50	$176.50
Purchase #2	$106.89	11.224%	$118.8873	$118.89	$118.90	$118.90
Purchase #3	$127.83	10.693%	$141.4989	$141.50	$141.50	$141.50
Purchase #4	$198.89	3.809%	$206.4657	$206.47	$206.45	$206.50
Purchase #5	$128.67	7.124%	$137.8365	$137.84	$137.85	$137.80
Purchase #6	$188.98	13.672%	$214.8173	$214.82	$214.80	$214.80
Purchase #7	$21.84	12.351%	$24.5375	$24.54	$24.55	$24.50
7 purchase totals =	$938.76		$1,020.5572	$1,020.57	$1,020.55	$1,020.50