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	$147.27	13.720%	$167.4754	$167.48	$167.50	$167.50
Purchase #2	$183.53	3.238%	$189.4727	$189.47	$189.45	$189.50
Purchase #3	$176.54	4.805%	$185.0227	$185.02	$185.00	$185.00
Purchase #4	$11.63	10.179%	$12.8138	$12.81	$12.80	$12.80
Purchase #5	$205.66	4.867%	$215.6695	$215.67	$215.65	$215.70
Purchase #6	$243.47	7.235%	$261.0851	$261.09	$261.10	$261.10
Purchase #7	$164.96	8.703%	$179.3165	$179.32	$179.30	$179.30
7 purchase totals =	$1,133.06		$1,210.8557	$1,210.86	$1,210.80	$1,210.90