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	$248.82	13.170%	$281.5896	$281.59	$281.60	$281.60
Purchase #2	$72.37	5.770%	$76.5457	$76.55	$76.55	$76.50
Purchase #3	$106.72	13.209%	$120.8166	$120.82	$120.80	$120.80
Purchase #4	$80.27	13.421%	$91.043	$91.04	$91.05	$91.00
Purchase #5	$165.53	9.527%	$181.3	$181.30	$181.30	$181.30
Purchase #6	$53.59	11.136%	$59.5578	$59.56	$59.55	$59.60
Purchase #7	$71.92	7.113%	$77.0357	$77.04	$77.05	$77.00
7 purchase totals =	$799.22		$887.8884	$887.90	$887.90	$887.80