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	$82.45	8.713%	$89.6339	$89.63	$89.65	$89.60
Purchase #2	$42.31	12.332%	$47.5277	$47.53	$47.55	$47.50
Purchase #3	$222.86	11.693%	$248.919	$248.92	$248.90	$248.90
Purchase #4	$18.27	10.503%	$20.1889	$20.19	$20.20	$20.20
Purchase #5	$168.77	12.864%	$190.4806	$190.48	$190.50	$190.50
Purchase #6	$140.55	8.107%	$151.9444	$151.94	$151.95	$151.90
Purchase #7	$168.68	5.781%	$178.4314	$178.43	$178.45	$178.40
7 purchase totals =	$843.89		$927.1259	$927.12	$927.20	$927.00