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	$47.34	3.263%	$48.8847	$48.88	$48.90	$48.90
Purchase #2	$242.49	5.805%	$256.5665	$256.57	$256.55	$256.60
Purchase #3	$76.35	13.772%	$86.8649	$86.86	$86.85	$86.90
Purchase #4	$172.77	9.730%	$189.5805	$189.58	$189.60	$189.60
Purchase #5	$29.47	6.598%	$31.4144	$31.41	$31.40	$31.40
Purchase #6	$193.63	9.756%	$212.5205	$212.52	$212.50	$212.50
Purchase #7	$69.33	13.467%	$78.6667	$78.67	$78.65	$78.70
7 purchase totals =	$831.38		$904.4982	$904.49	$904.45	$904.60