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	$89.92	12.119%	$100.8174	$100.82	$100.80	$100.80
Purchase #2	$224.86	8.809%	$244.6679	$244.67	$244.65	$244.70
Purchase #3	$116.83	9.780%	$128.256	$128.26	$128.25	$128.30
Purchase #4	$32.62	11.140%	$36.2539	$36.25	$36.25	$36.30
Purchase #5	$237.57	4.855%	$249.104	$249.10	$249.10	$249.10
Purchase #6	$157.59	6.303%	$167.5229	$167.52	$167.50	$167.50
Purchase #7	$232.62	12.833%	$262.4721	$262.47	$262.45	$262.50
7 purchase totals =	$1,092.01		$1,189.0942	$1,189.09	$1,189.00	$1,189.20