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	$32.71	3.713%	$33.9245	$33.92	$33.90	$33.90
Purchase #2	$132.74	10.276%	$146.3804	$146.38	$146.40	$146.40
Purchase #3	$98.64	13.221%	$111.6812	$111.68	$111.70	$111.70
Purchase #4	$27.61	9.866%	$30.334	$30.33	$30.35	$30.30
Purchase #5	$175.43	8.582%	$190.4854	$190.49	$190.50	$190.50
Purchase #6	$219.88	3.607%	$227.8111	$227.81	$227.80	$227.80
Purchase #7	$41.43	7.624%	$44.5886	$44.59	$44.60	$44.60
7 purchase totals =	$728.44		$785.2052	$785.20	$785.25	$785.20