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	$248.98	13.789%	$283.3119	$283.31	$283.30	$283.30
Purchase #2	$246.59	4.124%	$256.7594	$256.76	$256.75	$256.80
Purchase #3	$161.40	6.362%	$171.6683	$171.67	$171.65	$171.70
Purchase #4	$167.30	11.638%	$186.7704	$186.77	$186.75	$186.80
Purchase #5	$105.67	9.807%	$116.0331	$116.03	$116.05	$116.00
Purchase #6	$19.54	4.808%	$20.4795	$20.48	$20.50	$20.50
Purchase #7	$51.61	7.406%	$55.4322	$55.43	$55.45	$55.40
7 purchase totals =	$1,001.09		$1,090.4548	$1,090.45	$1,090.45	$1,090.50