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	$219.91	8.629%	$238.886	$238.89	$238.90	$238.90
Purchase #2	$205.27	4.511%	$214.5297	$214.53	$214.55	$214.50
Purchase #3	$181.61	13.195%	$205.5734	$205.57	$205.55	$205.60
Purchase #4	$123.54	12.626%	$139.1382	$139.14	$139.15	$139.10
Purchase #5	$85.89	5.308%	$90.449	$90.45	$90.45	$90.40
Purchase #6	$13.60	5.185%	$14.3052	$14.31	$14.30	$14.30
Purchase #7	$87.96	8.505%	$95.441	$95.44	$95.45	$95.40
7 purchase totals =	$917.78		$998.3225	$998.33	$998.35	$998.20