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	$130.58	5.260%	$137.4485	$137.45	$137.45	$137.40
Purchase #2	$45.54	12.229%	$51.1091	$51.11	$51.10	$51.10
Purchase #3	$50.45	7.514%	$54.2408	$54.24	$54.25	$54.20
Purchase #4	$213.60	11.712%	$238.6168	$238.62	$238.60	$238.60
Purchase #5	$119.87	5.867%	$126.9028	$126.90	$126.90	$126.90
Purchase #6	$146.88	7.533%	$157.9445	$157.94	$157.95	$157.90
Purchase #7	$92.54	10.554%	$102.3067	$102.31	$102.30	$102.30
7 purchase totals =	$799.46		$868.5692	$868.57	$868.55	$868.40