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	$52.59	6.660%	$56.0925	$56.09	$56.10	$56.10
Purchase #2	$25.37	13.847%	$28.883	$28.88	$28.90	$28.90
Purchase #3	$77.40	6.620%	$82.5239	$82.52	$82.50	$82.50
Purchase #4	$157.91	7.497%	$169.7485	$169.75	$169.75	$169.70
Purchase #5	$187.57	10.775%	$207.7807	$207.78	$207.80	$207.80
Purchase #6	$131.59	6.168%	$139.7065	$139.71	$139.70	$139.70
Purchase #7	$92.54	3.560%	$95.8344	$95.83	$95.85	$95.80
7 purchase totals =	$724.97		$780.5695	$780.56	$780.60	$780.50