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	$201.39	11.579%	$224.7089	$224.71	$224.70	$224.70
Purchase #2	$177.91	5.283%	$187.309	$187.31	$187.30	$187.30
Purchase #3	$106.32	3.320%	$109.8498	$109.85	$109.85	$109.80
Purchase #4	$38.39	5.105%	$40.3498	$40.35	$40.35	$40.30
Purchase #5	$245.86	9.353%	$268.8553	$268.86	$268.85	$268.90
Purchase #6	$244.84	12.377%	$275.1438	$275.14	$275.15	$275.10
Purchase #7	$135.55	6.762%	$144.7159	$144.72	$144.70	$144.70
7 purchase totals =	$1,150.26		$1,250.9325	$1,250.94	$1,250.90	$1,250.80