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	$231.79	11.492%	$258.4273	$258.43	$258.45	$258.40
Purchase #2	$134.48	10.733%	$148.9137	$148.91	$148.90	$148.90
Purchase #3	$14.27	11.454%	$15.9045	$15.90	$15.90	$15.90
Purchase #4	$42.59	7.697%	$45.8682	$45.87	$45.85	$45.90
Purchase #5	$82.31	5.304%	$86.6757	$86.68	$86.70	$86.70
Purchase #6	$89.84	3.404%	$92.8982	$92.90	$92.90	$92.90
Purchase #7	$40.49	10.401%	$44.7014	$44.70	$44.70	$44.70
7 purchase totals =	$635.77		$693.3890	$693.39	$693.40	$693.40