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	$73.70	12.174%	$82.6722	$82.67	$82.65	$82.70
Purchase #2	$201.37	7.476%	$216.4244	$216.42	$216.40	$216.40
Purchase #3	$101.88	6.682%	$108.6876	$108.69	$108.70	$108.70
Purchase #4	$33.51	10.675%	$37.0872	$37.09	$37.10	$37.10
Purchase #5	$70.58	3.293%	$72.9042	$72.90	$72.90	$72.90
Purchase #6	$137.67	9.839%	$151.2154	$151.22	$151.20	$151.20
Purchase #7	$152.86	9.257%	$167.0103	$167.01	$167.00	$167.00
7 purchase totals =	$771.57		$836.0013	$836.00	$835.95	$836.00