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	$49.64	12.453%	$55.8217	$55.82	$55.80	$55.80
Purchase #2	$30.61	8.843%	$33.3168	$33.32	$33.30	$33.30
Purchase #3	$246.55	13.693%	$280.3101	$280.31	$280.30	$280.30
Purchase #4	$226.28	6.400%	$240.7619	$240.76	$240.75	$240.80
Purchase #5	$89.42	8.266%	$96.8115	$96.81	$96.80	$96.80
Purchase #6	$72.64	6.657%	$77.4756	$77.48	$77.50	$77.50
Purchase #7	$83.95	6.321%	$89.2565	$89.26	$89.25	$89.30
7 purchase totals =	$799.09		$873.7541	$873.76	$873.70	$873.80