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	$141.61	4.871%	$148.5078	$148.51	$148.50	$148.50
Purchase #2	$190.56	8.378%	$206.5251	$206.53	$206.55	$206.50
Purchase #3	$245.56	13.503%	$278.718	$278.72	$278.70	$278.70
Purchase #4	$217.98	10.839%	$241.6069	$241.61	$241.60	$241.60
Purchase #5	$148.77	11.128%	$165.3251	$165.33	$165.35	$165.30
Purchase #6	$55.83	6.717%	$59.5801	$59.58	$59.60	$59.60
Purchase #7	$71.45	11.151%	$79.4174	$79.42	$79.40	$79.40
7 purchase totals =	$1,071.76		$1,179.6804	$1,179.70	$1,179.70	$1,179.60