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	$101.39	10.116%	$111.6466	$111.65	$111.65	$111.60
Purchase #2	$45.72	4.719%	$47.8775	$47.88	$47.90	$47.90
Purchase #3	$205.63	9.765%	$225.7098	$225.71	$225.70	$225.70
Purchase #4	$109.30	3.240%	$112.8413	$112.84	$112.85	$112.80
Purchase #5	$210.63	4.453%	$220.0094	$220.01	$220.00	$220.00
Purchase #6	$113.49	9.392%	$124.149	$124.15	$124.15	$124.10
Purchase #7	$150.30	3.815%	$156.0339	$156.03	$156.05	$156.00
7 purchase totals =	$936.46		$998.2675	$998.27	$998.30	$998.10