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	$10.38	11.263%	$11.5491	$11.55	$11.55	$11.50
Purchase #2	$164.32	6.454%	$174.9252	$174.93	$174.95	$174.90
Purchase #3	$120.77	7.265%	$129.5439	$129.54	$129.55	$129.50
Purchase #4	$93.26	5.709%	$98.5842	$98.58	$98.60	$98.60
Purchase #5	$228.70	12.215%	$256.6357	$256.64	$256.65	$256.60
Purchase #6	$72.35	7.117%	$77.4991	$77.50	$77.50	$77.50
Purchase #7	$72.45	8.482%	$78.5952	$78.60	$78.60	$78.60
7 purchase totals =	$762.23		$827.3324	$827.34	$827.40	$827.20