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	$93.85	12.376%	$105.4649	$105.46	$105.45	$105.50
Purchase #2	$157.55	13.730%	$179.1816	$179.18	$179.20	$179.20
Purchase #3	$88.91	11.826%	$99.4245	$99.42	$99.40	$99.40
Purchase #4	$149.48	13.473%	$169.6194	$169.62	$169.60	$169.60
Purchase #5	$13.84	11.442%	$15.4236	$15.42	$15.40	$15.40
Purchase #6	$118.55	4.654%	$124.0673	$124.07	$124.05	$124.10
Purchase #7	$246.37	13.780%	$280.3198	$280.32	$280.30	$280.30
7 purchase totals =	$868.55		$973.5011	$973.49	$973.40	$973.50