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	$123.37	12.495%	$138.7851	$138.79	$138.80	$138.80
Purchase #2	$141.64	8.443%	$153.5987	$153.60	$153.60	$153.60
Purchase #3	$180.35	10.160%	$198.6736	$198.67	$198.65	$198.70
Purchase #4	$179.68	9.136%	$196.0956	$196.10	$196.10	$196.10
Purchase #5	$239.71	11.869%	$268.1612	$268.16	$268.15	$268.20
Purchase #6	$218.96	8.819%	$238.2701	$238.27	$238.25	$238.30
Purchase #7	$131.35	6.495%	$139.8812	$139.88	$139.90	$139.90
7 purchase totals =	$1,215.06		$1,333.4655	$1,333.47	$1,333.45	$1,333.60