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	$132.28	3.626%	$137.0765	$137.08	$137.10	$137.10
Purchase #2	$144.55	4.475%	$151.0186	$151.02	$151.00	$151.00
Purchase #3	$240.38	12.452%	$270.3121	$270.31	$270.30	$270.30
Purchase #4	$212.32	13.253%	$240.4588	$240.46	$240.45	$240.50
Purchase #5	$59.99	10.627%	$66.3651	$66.37	$66.35	$66.40
Purchase #6	$48.51	9.366%	$53.0534	$53.05	$53.05	$53.10
Purchase #7	$71.90	9.218%	$78.5277	$78.53	$78.55	$78.50
7 purchase totals =	$909.93		$996.8122	$996.82	$996.80	$996.90