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	$28.59	11.593%	$31.9044	$31.90	$31.90	$31.90
Purchase #2	$214.38	12.348%	$240.8516	$240.85	$240.85	$240.90
Purchase #3	$97.54	7.515%	$104.8701	$104.87	$104.85	$104.90
Purchase #4	$168.61	12.727%	$190.069	$190.07	$190.05	$190.10
Purchase #5	$231.31	11.619%	$258.1859	$258.19	$258.20	$258.20
Purchase #6	$28.46	12.318%	$31.9657	$31.97	$31.95	$32.00
Purchase #7	$156.81	5.565%	$165.5365	$165.54	$165.55	$165.50
7 purchase totals =	$925.70		$1,023.3832	$1,023.39	$1,023.35	$1,023.50