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	$27.39	5.220%	$28.8198	$28.82	$28.80	$28.80
Purchase #2	$33.83	13.284%	$38.324	$38.32	$38.30	$38.30
Purchase #3	$141.69	6.166%	$150.4266	$150.43	$150.45	$150.40
Purchase #4	$78.44	4.738%	$82.1565	$82.16	$82.15	$82.20
Purchase #5	$89.70	4.324%	$93.5786	$93.58	$93.60	$93.60
Purchase #6	$247.60	13.121%	$280.0876	$280.09	$280.10	$280.10
Purchase #7	$138.98	6.353%	$147.8094	$147.81	$147.80	$147.80
7 purchase totals =	$757.63		$821.2025	$821.21	$821.20	$821.20