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	$241.68	13.197%	$273.5745	$273.57	$273.55	$273.60
Purchase #2	$160.61	8.767%	$174.6907	$174.69	$174.70	$174.70
Purchase #3	$21.76	3.187%	$22.4535	$22.45	$22.45	$22.50
Purchase #4	$133.32	13.463%	$151.2689	$151.27	$151.25	$151.30
Purchase #5	$29.30	7.171%	$31.4011	$31.40	$31.40	$31.40
Purchase #6	$176.65	13.323%	$200.1851	$200.19	$200.20	$200.20
Purchase #7	$94.54	11.476%	$105.3894	$105.39	$105.40	$105.40
7 purchase totals =	$857.86		$958.9632	$958.96	$958.95	$959.10