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	$72.56	13.452%	$82.3208	$82.32	$82.30	$82.30
Purchase #2	$47.57	6.193%	$50.516	$50.52	$50.50	$50.50
Purchase #3	$86.40	11.130%	$96.0163	$96.02	$96.00	$96.00
Purchase #4	$154.31	4.258%	$160.8805	$160.88	$160.90	$160.90
Purchase #5	$179.25	3.381%	$185.3104	$185.31	$185.30	$185.30
Purchase #6	$236.38	8.579%	$256.659	$256.66	$256.65	$256.70
Purchase #7	$77.42	12.480%	$87.082	$87.08	$87.10	$87.10
7 purchase totals =	$853.89		$918.7850	$918.79	$918.75	$918.80