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	$146.42	7.192%	$156.9505	$156.95	$156.95	$157.00
Purchase #2	$167.41	13.246%	$189.5851	$189.59	$189.60	$189.60
Purchase #3	$135.88	11.874%	$152.0144	$152.01	$152.00	$152.00
Purchase #4	$241.75	3.725%	$250.7552	$250.76	$250.75	$250.80
Purchase #5	$208.50	6.286%	$221.6063	$221.61	$221.60	$221.60
Purchase #6	$173.70	13.328%	$196.8507	$196.85	$196.85	$196.90
Purchase #7	$135.83	4.863%	$142.4354	$142.44	$142.45	$142.40
7 purchase totals =	$1,209.49		$1,310.1976	$1,310.21	$1,310.20	$1,310.30