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	$129.79	5.421%	$136.8259	$136.83	$136.85	$136.80
Purchase #2	$147.47	12.865%	$166.442	$166.44	$166.45	$166.40
Purchase #3	$124.64	6.872%	$133.2053	$133.21	$133.20	$133.20
Purchase #4	$114.93	7.710%	$123.7911	$123.79	$123.80	$123.80
Purchase #5	$172.38	4.408%	$179.9785	$179.98	$180.00	$180.00
Purchase #6	$213.47	10.251%	$235.3528	$235.35	$235.35	$235.40
Purchase #7	$102.90	8.174%	$111.311	$111.31	$111.30	$111.30
7 purchase totals =	$1,005.58		$1,086.9066	$1,086.91	$1,086.95	$1,086.90