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	$150.54	11.835%	$168.3564	$168.36	$168.35	$168.40
Purchase #2	$99.87	8.800%	$108.6586	$108.66	$108.65	$108.70
Purchase #3	$179.54	9.322%	$196.2767	$196.28	$196.30	$196.30
Purchase #4	$238.44	8.789%	$259.3965	$259.40	$259.40	$259.40
Purchase #5	$218.39	10.721%	$241.8036	$241.80	$241.80	$241.80
Purchase #6	$227.88	12.736%	$256.9028	$256.90	$256.90	$256.90
Purchase #7	$46.54	13.397%	$52.775	$52.78	$52.80	$52.80
7 purchase totals =	$1,161.20		$1,284.1696	$1,284.18	$1,284.20	$1,284.30