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	$91.55	9.435%	$100.1877	$100.19	$100.20	$100.20
Purchase #2	$83.70	9.275%	$91.4632	$91.46	$91.45	$91.50
Purchase #3	$64.55	12.389%	$72.5471	$72.55	$72.55	$72.50
Purchase #4	$165.53	9.734%	$181.6427	$181.64	$181.65	$181.60
Purchase #5	$171.79	9.247%	$187.6754	$187.68	$187.70	$187.70
Purchase #6	$55.63	10.374%	$61.4011	$61.40	$61.40	$61.40
Purchase #7	$196.70	10.363%	$217.084	$217.08	$217.10	$217.10
7 purchase totals =	$829.45		$912.0012	$912.00	$912.05	$912.00