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	$125.50	11.109%	$139.4418	$139.44	$139.45	$139.40
Purchase #2	$204.31	7.104%	$218.8242	$218.82	$218.80	$218.80
Purchase #3	$167.30	8.601%	$181.6895	$181.69	$181.70	$181.70
Purchase #4	$73.81	6.355%	$78.5006	$78.50	$78.50	$78.50
Purchase #5	$23.42	13.811%	$26.6545	$26.65	$26.65	$26.70
Purchase #6	$194.54	12.354%	$218.5735	$218.57	$218.55	$218.60
Purchase #7	$111.51	4.529%	$116.5603	$116.56	$116.55	$116.60
7 purchase totals =	$900.39		$980.2444	$980.23	$980.20	$980.30