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	$222.57	3.564%	$230.5024	$230.50	$230.50	$230.50
Purchase #2	$142.82	5.557%	$150.7565	$150.76	$150.75	$150.80
Purchase #3	$246.69	13.551%	$280.119	$280.12	$280.10	$280.10
Purchase #4	$141.48	11.123%	$157.2168	$157.22	$157.20	$157.20
Purchase #5	$48.34	10.219%	$53.2799	$53.28	$53.30	$53.30
Purchase #6	$69.71	11.219%	$77.5308	$77.53	$77.55	$77.50
Purchase #7	$163.82	6.355%	$174.2308	$174.23	$174.25	$174.20
7 purchase totals =	$1,035.43		$1,123.6362	$1,123.64	$1,123.65	$1,123.60