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	$44.59	13.344%	$50.5401	$50.54	$50.55	$50.50
Purchase #2	$166.72	4.603%	$174.3941	$174.39	$174.40	$174.40
Purchase #3	$216.46	3.414%	$223.8499	$223.85	$223.85	$223.80
Purchase #4	$169.79	6.495%	$180.8179	$180.82	$180.80	$180.80
Purchase #5	$11.36	9.541%	$12.4439	$12.44	$12.45	$12.40
Purchase #6	$164.86	10.789%	$182.6467	$182.65	$182.65	$182.60
Purchase #7	$74.67	10.650%	$82.6224	$82.62	$82.60	$82.60
7 purchase totals =	$848.45		$907.3150	$907.31	$907.30	$907.10