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	$120.64	13.222%	$136.591	$136.59	$136.60	$136.60
Purchase #2	$98.81	9.374%	$108.0724	$108.07	$108.05	$108.10
Purchase #3	$220.59	9.714%	$242.0181	$242.02	$242.00	$242.00
Purchase #4	$69.39	12.828%	$78.2913	$78.29	$78.30	$78.30
Purchase #5	$156.41	13.488%	$177.5066	$177.51	$177.50	$177.50
Purchase #6	$177.83	10.205%	$195.9776	$195.98	$196.00	$196.00
Purchase #7	$62.92	10.291%	$69.3951	$69.40	$69.40	$69.40
7 purchase totals =	$906.59		$1,007.8521	$1,007.86	$1,007.85	$1,007.90