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	$144.25	10.342%	$159.1683	$159.17	$159.15	$159.20
Purchase #2	$149.69	11.731%	$167.2501	$167.25	$167.25	$167.30
Purchase #3	$37.29	11.120%	$41.4366	$41.44	$41.45	$41.40
Purchase #4	$123.67	12.808%	$139.5097	$139.51	$139.50	$139.50
Purchase #5	$238.36	5.339%	$251.086	$251.09	$251.10	$251.10
Purchase #6	$79.43	12.340%	$89.2317	$89.23	$89.25	$89.20
Purchase #7	$86.44	3.408%	$89.3859	$89.39	$89.40	$89.40
7 purchase totals =	$859.13		$937.0683	$937.08	$937.10	$937.10