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	$108.82	10.583%	$120.3364	$120.34	$120.35	$120.30
Purchase #2	$90.36	13.432%	$102.4972	$102.50	$102.50	$102.50
Purchase #3	$209.96	4.757%	$219.9478	$219.95	$219.95	$219.90
Purchase #4	$52.51	7.115%	$56.2461	$56.25	$56.25	$56.20
Purchase #5	$148.31	7.784%	$159.8545	$159.85	$159.85	$159.90
Purchase #6	$201.56	6.123%	$213.9015	$213.90	$213.90	$213.90
Purchase #7	$109.46	13.164%	$123.8693	$123.87	$123.85	$123.90
7 purchase totals =	$920.98		$996.6528	$996.66	$996.65	$996.60