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	$83.93	4.716%	$87.8881	$87.89	$87.90	$87.90
Purchase #2	$40.40	7.797%	$43.55	$43.55	$43.55	$43.60
Purchase #3	$131.50	11.283%	$146.3371	$146.34	$146.35	$146.30
Purchase #4	$151.35	6.593%	$161.3285	$161.33	$161.35	$161.30
Purchase #5	$57.68	13.373%	$65.3935	$65.39	$65.40	$65.40
Purchase #6	$118.46	4.173%	$123.4033	$123.40	$123.40	$123.40
Purchase #7	$47.32	9.714%	$51.9167	$51.92	$51.90	$51.90
7 purchase totals =	$630.64		$679.8172	$679.82	$679.85	$679.80