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	$111.85	7.657%	$120.4144	$120.41	$120.40	$120.40
Purchase #2	$242.78	4.662%	$254.0984	$254.10	$254.10	$254.10
Purchase #3	$23.52	13.191%	$26.6225	$26.62	$26.60	$26.60
Purchase #4	$25.39	7.215%	$27.2219	$27.22	$27.20	$27.20
Purchase #5	$250.77	11.843%	$280.4687	$280.47	$280.45	$280.50
Purchase #6	$152.94	5.180%	$160.8623	$160.86	$160.85	$160.90
Purchase #7	$51.65	3.506%	$53.4608	$53.46	$53.45	$53.50
7 purchase totals =	$858.90		$923.1490	$923.14	$923.05	$923.20