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	$244.89	13.782%	$278.6407	$278.64	$278.65	$278.60
Purchase #2	$125.48	8.388%	$136.0053	$136.01	$136.00	$136.00
Purchase #3	$241.88	11.630%	$270.0106	$270.01	$270.00	$270.00
Purchase #4	$202.81	9.512%	$222.1013	$222.10	$222.10	$222.10
Purchase #5	$226.43	5.320%	$238.4761	$238.48	$238.50	$238.50
Purchase #6	$151.30	13.760%	$172.1189	$172.12	$172.10	$172.10
Purchase #7	$248.42	4.111%	$258.6325	$258.63	$258.65	$258.60
7 purchase totals =	$1,441.21		$1,575.9854	$1,575.99	$1,576.00	$1,575.90