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	$102.51	13.706%	$116.56	$116.56	$116.55	$116.60
Purchase #2	$85.29	4.826%	$89.4061	$89.41	$89.40	$89.40
Purchase #3	$63.70	11.761%	$71.1918	$71.19	$71.20	$71.20
Purchase #4	$196.63	5.184%	$206.8233	$206.82	$206.80	$206.80
Purchase #5	$105.63	6.460%	$112.4537	$112.45	$112.45	$112.50
Purchase #6	$99.25	3.812%	$103.0334	$103.03	$103.05	$103.00
Purchase #7	$243.85	8.847%	$265.4234	$265.42	$265.40	$265.40
7 purchase totals =	$896.86		$964.8917	$964.88	$964.85	$964.90