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	$127.56	3.202%	$131.6445	$131.64	$131.65	$131.60
Purchase #2	$201.46	3.377%	$208.2633	$208.26	$208.25	$208.30
Purchase #3	$205.42	12.735%	$231.5802	$231.58	$231.60	$231.60
Purchase #4	$34.98	8.408%	$37.9211	$37.92	$37.90	$37.90
Purchase #5	$7.47	5.181%	$7.857	$7.86	$7.85	$7.90
Purchase #6	$18.76	9.317%	$20.5079	$20.51	$20.50	$20.50
Purchase #7	$200.33	3.109%	$206.5583	$206.56	$206.55	$206.60
7 purchase totals =	$795.98		$844.3323	$844.33	$844.30	$844.40