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	$37.37	12.386%	$41.9986	$42.00	$42.00	$42.00
Purchase #2	$216.83	12.436%	$243.795	$243.80	$243.80	$243.80
Purchase #3	$225.50	6.320%	$239.7516	$239.75	$239.75	$239.80
Purchase #4	$177.89	9.558%	$194.8927	$194.89	$194.90	$194.90
Purchase #5	$73.50	12.298%	$82.539	$82.54	$82.55	$82.50
Purchase #6	$241.58	3.768%	$250.6827	$250.68	$250.70	$250.70
Purchase #7	$178.64	3.422%	$184.7531	$184.75	$184.75	$184.80
7 purchase totals =	$1,151.31		$1,238.4127	$1,238.41	$1,238.45	$1,238.50