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	$11.80	13.303%	$13.3698	$13.37	$13.35	$13.40
Purchase #2	$43.28	5.498%	$45.6595	$45.66	$45.65	$45.70
Purchase #3	$230.36	3.641%	$238.7474	$238.75	$238.75	$238.70
Purchase #4	$250.49	9.208%	$273.5551	$273.56	$273.55	$273.60
Purchase #5	$207.52	4.817%	$217.5162	$217.52	$217.50	$217.50
Purchase #6	$90.33	12.328%	$101.4659	$101.47	$101.45	$101.50
Purchase #7	$172.91	5.349%	$182.159	$182.16	$182.15	$182.20
7 purchase totals =	$1,006.69		$1,072.4729	$1,072.49	$1,072.40	$1,072.60