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	$238.79	6.684%	$254.7507	$254.75	$254.75	$254.80
Purchase #2	$103.54	3.352%	$107.0107	$107.01	$107.00	$107.00
Purchase #3	$248.53	7.810%	$267.9402	$267.94	$267.95	$267.90
Purchase #4	$28.37	10.552%	$31.3636	$31.36	$31.35	$31.40
Purchase #5	$48.75	10.654%	$53.9438	$53.94	$53.95	$53.90
Purchase #6	$208.83	5.553%	$220.4263	$220.43	$220.45	$220.40
Purchase #7	$90.59	10.508%	$100.1092	$100.11	$100.10	$100.10
7 purchase totals =	$967.40		$1,035.5445	$1,035.54	$1,035.55	$1,035.50