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	$178.37	5.288%	$187.8022	$187.80	$187.80	$187.80
Purchase #2	$34.88	8.822%	$37.9571	$37.96	$37.95	$38.00
Purchase #3	$224.89	3.226%	$232.145	$232.15	$232.15	$232.10
Purchase #4	$91.37	8.715%	$99.3329	$99.33	$99.35	$99.30
Purchase #5	$17.55	6.366%	$18.6672	$18.67	$18.65	$18.70
Purchase #6	$89.28	6.694%	$95.2564	$95.26	$95.25	$95.30
Purchase #7	$37.70	12.232%	$42.3115	$42.31	$42.30	$42.30
7 purchase totals =	$674.04		$713.4723	$713.48	$713.45	$713.50