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	$136.50	3.370%	$141.1001	$141.10	$141.10	$141.10
Purchase #2	$240.88	13.561%	$273.5457	$273.55	$273.55	$273.50
Purchase #3	$249.95	12.240%	$280.5439	$280.54	$280.55	$280.50
Purchase #4	$189.59	3.205%	$195.6664	$195.67	$195.65	$195.70
Purchase #5	$92.95	8.735%	$101.0692	$101.07	$101.05	$101.10
Purchase #6	$166.78	9.454%	$182.5474	$182.55	$182.55	$182.50
Purchase #7	$203.33	10.789%	$225.2673	$225.27	$225.25	$225.30
7 purchase totals =	$1,279.98		$1,399.7400	$1,399.75	$1,399.70	$1,399.70