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	$137.88	10.392%	$152.2085	$152.21	$152.20	$152.20
Purchase #2	$225.78	3.314%	$233.2623	$233.26	$233.25	$233.30
Purchase #3	$158.47	11.228%	$176.263	$176.26	$176.25	$176.30
Purchase #4	$110.39	7.128%	$118.2586	$118.26	$118.25	$118.30
Purchase #5	$72.49	12.448%	$81.5136	$81.51	$81.50	$81.50
Purchase #6	$170.52	5.308%	$179.5712	$179.57	$179.55	$179.60
Purchase #7	$131.27	10.826%	$145.4813	$145.48	$145.50	$145.50
7 purchase totals =	$1,006.80		$1,086.5585	$1,086.55	$1,086.50	$1,086.70