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	$180.57	6.269%	$191.8899	$191.89	$191.90	$191.90
Purchase #2	$112.52	7.363%	$120.8048	$120.80	$120.80	$120.80
Purchase #3	$87.41	9.183%	$95.4369	$95.44	$95.45	$95.40
Purchase #4	$177.27	12.523%	$199.4695	$199.47	$199.45	$199.50
Purchase #5	$84.75	4.629%	$88.6731	$88.67	$88.65	$88.70
Purchase #6	$29.88	5.312%	$31.4672	$31.47	$31.45	$31.50
Purchase #7	$95.87	10.150%	$105.6008	$105.60	$105.60	$105.60
7 purchase totals =	$768.27		$833.3422	$833.34	$833.30	$833.40