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	$135.39	11.310%	$150.7026	$150.70	$150.70	$150.70
Purchase #2	$244.55	11.638%	$273.0107	$273.01	$273.00	$273.00
Purchase #3	$89.65	3.597%	$92.8747	$92.87	$92.85	$92.90
Purchase #4	$78.90	8.507%	$85.612	$85.61	$85.60	$85.60
Purchase #5	$226.86	9.614%	$248.6703	$248.67	$248.65	$248.70
Purchase #6	$11.51	5.570%	$12.1511	$12.15	$12.15	$12.20
Purchase #7	$220.72	6.867%	$235.8768	$235.88	$235.90	$235.90
7 purchase totals =	$1,007.58		$1,098.8982	$1,098.89	$1,098.85	$1,099.00