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	$78.98	6.228%	$83.8989	$83.90	$83.90	$83.90
Purchase #2	$56.70	9.322%	$61.9856	$61.99	$62.00	$62.00
Purchase #3	$198.69	7.144%	$212.8844	$212.88	$212.90	$212.90
Purchase #4	$249.35	10.787%	$276.2474	$276.25	$276.25	$276.20
Purchase #5	$117.49	4.609%	$122.9051	$122.91	$122.90	$122.90
Purchase #6	$249.87	10.659%	$276.5036	$276.50	$276.50	$276.50
Purchase #7	$123.44	6.560%	$131.5377	$131.54	$131.55	$131.50
7 purchase totals =	$1,074.52		$1,165.9627	$1,165.97	$1,166.00	$1,165.90