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	$244.45	13.458%	$277.3481	$277.35	$277.35	$277.30
Purchase #2	$176.93	7.353%	$189.9397	$189.94	$189.95	$189.90
Purchase #3	$98.76	6.400%	$105.0806	$105.08	$105.10	$105.10
Purchase #4	$197.88	11.699%	$221.03	$221.03	$221.05	$221.00
Purchase #5	$85.45	6.554%	$91.0504	$91.05	$91.05	$91.10
Purchase #6	$61.84	11.790%	$69.1309	$69.13	$69.15	$69.10
Purchase #7	$186.70	5.305%	$196.6044	$196.60	$196.60	$196.60
7 purchase totals =	$1,052.01		$1,150.1841	$1,150.18	$1,150.25	$1,150.10