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	$229.94	5.619%	$242.8603	$242.86	$242.85	$242.90
Purchase #2	$140.58	11.566%	$156.8395	$156.84	$156.85	$156.80
Purchase #3	$183.60	8.637%	$199.4575	$199.46	$199.45	$199.50
Purchase #4	$231.41	4.514%	$241.8558	$241.86	$241.85	$241.90
Purchase #5	$75.70	12.666%	$85.2882	$85.29	$85.30	$85.30
Purchase #6	$220.56	9.246%	$240.953	$240.95	$240.95	$241.00
Purchase #7	$158.72	12.168%	$178.033	$178.03	$178.05	$178.00
7 purchase totals =	$1,240.51		$1,345.2873	$1,345.29	$1,345.30	$1,345.40