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	$187.79	6.818%	$200.5935	$200.59	$200.60	$200.60
Purchase #2	$135.50	5.703%	$143.2276	$143.23	$143.25	$143.20
Purchase #3	$190.80	12.666%	$214.9667	$214.97	$214.95	$215.00
Purchase #4	$60.35	12.104%	$67.6548	$67.65	$67.65	$67.70
Purchase #5	$89.65	6.600%	$95.5669	$95.57	$95.55	$95.60
Purchase #6	$26.45	9.823%	$29.0482	$29.05	$29.05	$29.00
Purchase #7	$55.83	6.244%	$59.316	$59.32	$59.30	$59.30
7 purchase totals =	$746.37		$810.3737	$810.38	$810.35	$810.40