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	$14.84	11.697%	$16.5758	$16.58	$16.60	$16.60
Purchase #2	$103.73	10.452%	$114.5719	$114.57	$114.55	$114.60
Purchase #3	$125.50	7.468%	$134.8723	$134.87	$134.85	$134.90
Purchase #4	$19.30	8.308%	$20.9034	$20.90	$20.90	$20.90
Purchase #5	$128.95	6.799%	$137.7173	$137.72	$137.70	$137.70
Purchase #6	$89.30	5.140%	$93.89	$93.89	$93.90	$93.90
Purchase #7	$17.89	3.293%	$18.4791	$18.48	$18.50	$18.50
7 purchase totals =	$499.51		$537.0098	$537.01	$537.00	$537.10