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	$131.33	4.747%	$137.5642	$137.56	$137.55	$137.60
Purchase #2	$86.88	4.276%	$90.595	$90.60	$90.60	$90.60
Purchase #3	$73.55	11.855%	$82.2694	$82.27	$82.25	$82.30
Purchase #4	$196.81	5.849%	$208.3214	$208.32	$208.30	$208.30
Purchase #5	$53.32	9.721%	$58.5032	$58.50	$58.50	$58.50
Purchase #6	$149.94	7.607%	$161.3459	$161.35	$161.35	$161.30
Purchase #7	$226.99	11.656%	$253.448	$253.45	$253.45	$253.40
7 purchase totals =	$918.82		$992.0471	$992.05	$992.00	$992.00